Author's Note: A lot of you have noticed the ballooning cast of characters and the complexity of things, and I'm in agreement. Fortunately, the last chapter and this one are the 'hill' to climb over before things get back to the action. I also can't really get back to the action before I wrap this up and finally put all of Merlin's cards on the table, so I ask you to bear with me. For those wondering, Ereshkigal has a specific purpose that will be made clear later on and this might be the last chance to integrate her without it being odd for pacing. The one other new character shown in this chapter is unavoidable as well due to the canon lore, but the vast majority of the characters I had intended to appear in the Fourth Holy Grail War have either appeared by now or have been pushed to more appropriate places in the post-war timeline. The one remaining character I will have to introduce in this war can wait until some numbers have been culled.
aGnamZero: Thank you! When I considered giving Artoria a 'modern disguise', Mysterious Heroine X stood out as the perfect callback. Shirou's age is indeed listed as seventeen as of the beginning of Fate/stay night (January 31, 2004), though it must be remembered that this was only an estimation because he was an amnesiac in the canon whose previous identity and birthdate were lost. I had to look more at how the government would have estimated his age after the Fuyuki Fire to begin with and this would have been done by analyzing what surviving procedural memory he had retained from his schoolwork. This way, they could have learned what grade he was in before the fire. As a school student in Japan is always a certain age at the start of the school year in April (students always start elementary school in April of their sixth year), the best they could do was say "he is in grade x" and thus determine that "he was x years old as of last April". The best logic we reasonably have is that "Shirou Emiya was seventeen as of April 2003 because he is a second-year High School Student in January 2004". It would have been easiest for the government to define his birthday as late March 1987 or April 1, 1987 if only for the sake of administrative function (hence being listed as 17 in FSN) when he really could have been born at any point between April 2, 1986 and April 1, 1987. When looking at actual probability, it is five times more likely than not (ten months out of twelve had passed since April for him to have a birthday by January 31, 2004) that Shirou had turned eighteen by the time of Fate/stay Night.
Shirou's physical development as of Fate/stay Night is a small clue that he was born sooner rather than later in that window, so I have him as having has his birthday before November (and thus having turned eight by November 1994's Fate/Zero). However, it is by no means absolute. It is just the best I can do. Sooner or later, I have to commit to a birthday that will more than likely be wrong.
The 'accidental harem' description isn't set in stone, or even a statement that he'd be with multiple girls in the end. Saying it was more to cover my butt because Shirou will attract women by the mere act of being himself even if he doesn't actively encourage them. Strong in various ways, protective, kind, able to cook and fix almost anything, actually a decent person in a setting where most female Magi his age were raised starved for basic kindness...a harem or fan club is likely to form without his consent or knowledge. Fate/stay Night is even, to a large degree, about which girl he picks from that forming group. There is a reason the fandom says he has a 'Harem Protagonist EX' skill. Who he is with in the end will depend heavily on the natural flow of interactions and events, though Saber has the deck stacked in her favor for obvious reasons.
Sakura did not get her upgrades to be an extension of Shirou. Sakura got her upgrades because I felt she never had a chance to be anything but the damsel in distress and I want to see where she can go if taken in a different direction. The girl can do things the Tohsaka family never could, go places they can't reach, and that potential has previously been ignored. She is also a good rival for her sister to spur on Rin's growth as well. Also, the talk of Tokiomi marrying Shirou to Rin is more 'a starting point from which to explore his conflict between being a Magus and a father' rather than a promise of what will happen in the future. That will be explored in this chapter.
Chapter 17: Merlin Comes Clean
Shirou's Reality Marble
115 hours and 22 minutes to Zero
Shirou's Reality Marble had developed notably as of late to take a form resembling the general geography of Fuyuki. Only bits and pieces were fully defined as of yet, mostly locations that had been important to the being known as Shirou. Many locations other than this were still hazy and sometimes glitchy. The city itself couldn't even seem to decide if it was the Fuyuki City of 1994 or of 2004. The field of swords still existed, though it had moved to the area west of Fuyuki and north of Ryuudou Temple to replace what was previously farmland.
EMIYA rested on the roof of the Emiya Residence of 2004, one of the most clearly defined areas of the city. Controlling a Projected body in the 'real world' along with his true self in here had been a bit confusing at first, but he was starting to get the hang of it. A sudden surge of energy and a violent earthquake, however, disturbed him from the late morning relaxation. The former Counter Guardian was shaken from his perch on the roof and forced to transition from a roll into a half-controlled jump to the ground. In addition to feeling a massive addition to the Reality Marble, he felt a power on the scale of a Divine Spirit. No, he felt two, and one was charging toward him at full speed through the air.
The veteran Archer prepared for a fight by summoning a bow, alongside several arrow versions of Hrunting, and returning to the rooftops. His target high above him in the sky slowed and the Archer's eyes widened in clear surprise. Riding a large bow known as the Boat of Manna, which revealed to EMIYA the newcomer's true identity, was a seven-year-old Rin of all people. Or rather, a girl who borrowed Rin's appearance. Her eyes were red, momentarily flickering gold in anger as they regarded him. Her asymmetrical and ornate attire would have been scandalous on an older frame.
"You seem surprised to see me, bowman. It must not have been you. Point me to the one who dared to summon me, the one who sought to limit my Authority by trapping me in the form of a child, and I will spare you when I teach them the displeasure of the Mistress of Heaven!" This was Ishtar, the spurned suitor and enemy of Gilgamesh. She was also the spoiled Sumerian goddess of Venus, harvest, prosperity, war, destruction, love, beauty, lust, fertility, and pretty much any other supplemental Authority that her father could pamper her with. Of course, some of her Authorities did not play nice with her body's current youth and contributed to her fury. She was also pouring on the pompous attitude to intimidate EMIYA into compliance.
EMIYA had to fight his default instinct to give a snarky-but-caring response designed for the Tohsaka heiress. This was not the young woman he knew, but rather someone who could be a very different sort of trouble. "I can contact a person with a high-level Clairvoyance skill. He put me here without asking first and loves pranking people, so he either had a hand in this or can tell us who does. I also felt another Divine Spirit-level power show up at the same moment you did. You'll find the other power near the large beam of light lancing up into the sky. And yes, the light show's normal for this place."
Ishtar calmed slightly at the prospect of answers and looked in the indicated direction. Oh, she'd been aware of the beam of light. However, in her anger, confronting the first being she perceived in case they were an appropriate target of her fury felt more important than investigating the oddity. The other Divine Spirit's energy had been somewhat obscured from her awareness by a mix of the energy in that light and her own rage, but she quickly widened her eyes in recognition when she finally focused her senses on it. She then sped off without another word to EMIYA.
"...Just how often is that face going to cause trouble for me, anyway?" EMIYA asked himself before calling on Berserker's F-15J and leaping onto its wing mid-flight to follow the girl. He could have used Gilgamesh's Vimanna instead, but Ishtar's history with the King of Heroes made that a particularly bad idea.
Breaking the sound barrier, Ishtar had flown the distance from the Emiya Residence to Ryuudou Temple in under fifteen seconds. The aerial being had a greater sensory range than most and took full advantage of it to find her target below. Standing relatively close to the light connecting this place to the Reverse Side of the World, while peering into an out-of-place gold chalice sitting on the grassy ground, was a child with her blonde hair in twintails. She was studying its contents rather intently with inquisitive red eyes. The ornate black clothing with gold trim that she wore did not indicate human origin, nor did the red cloak that was around her shoulders. Her energy and the spear she carried were dead giveaways as to her identity even if her appearance had changed into something far more innocuous.
Ereshkigal blinked and finally felt a familiar sensation as Ishtar willfully descended into her range of perception. Looking up, she regarded her sister with red eyes that contained no malice. She made no aggressive moves. "Ishtar..." Ereshkigal's voice carried no resentment or condemnation.
"Ereshkigal." Ishtar's tone was more curt than her sister's and her attitude a bit wary. The girl's feet never fully touched the ground, but rather she hovered just a bit above it in a state of combat readiness. Ishtar had already died once to Ereshkigal when intruding on Kur to steal power from her and had no intention of letting it happen again.
"...d-did you do this, Ishtar? Did you arrange to save me?" Ereshkigal asked of her sister. Ishtar's guarded expression shifted into one of mild confusion. Before further words could be spoken, the sibling Divine Spirits heard the roar of a jet aircraft above. EMIYA leapt from the wing of the fighter and, with a burst of prana, slowed his landing enough to come to a stop unscathed. The F-15J broke apart into motes of light, willfully dismissed.
"I assume she isn't hostile then?" EMIYA asked Ishtar while rising and walking over to the pair. On noting that it was yet another Rin, EMIYA had to stop himself from groaning. "I'm an Archer-class Servant, and you probably know how we feel about giving out True Names. I guess you could call me the assigned guardian spirit of this place."
Ereshkigal gave a smile, simply happy to be free and talking to people. "I am Ereshkigal, Queen of Kur. I was trapped in my realm when I felt someone or something contact me. It wasn't in word as much as in feeling, but...it asked for a contract so that it might save me. I accepted before I even realized it. Now, Kur lay below us as part of...wherever we are."
"What? You accepted a contract?" Ishtar's eyes flashed gold in anger. "Don't you remember that we're split from the same Earth Mother Authority? Twin goddesses? When you accepted the contract, I got dragged in too! Now we're both leashed by some unknown force and stuck looking like...this!"
Ryuudou Temple
115 hours and 21 minutes to Zero
"HAHAHAHAHAHAHAHAHA!" The previously glowering Gilgamesh seated on the steps of the main building of Ryuudou Temple had rapidly changed facial expressions between surprise, intense focus, and finally uproarious laughter over the last two minutes without any apparent stimulus. Now, the uncomprehending Byakuya Matou scrambled behind the relative safety of the stoic and unmoving Hercules as the golden man engaged in what appeared to be a sudden and radical departure from reality.
It was as if the clairvoyant had heard the punchline to some great cosmic joke.
Avalon
The silence was palpable. Merlin had just told Artoria over the phone what Morgan had already been informed of; that Shirou was a gestalt of many souls rather than merely two. They were Shirous that had perished throughout assorted Parallel Worlds, mostly ones who had been under Artoria's care during the Fifth Holy Grail War. Thanks to enlisting the aid of a certain Second Magician who had been convinced that the outcome would be 'interesting', every soul from a 'bad end' timeline in AD 2004 was collected in one scabbard and eventually implanted into the modern Shirou's mother before his birth. Merlin had chosen to save as many Shirou as possible rather than only the one, well aware that Artoria would have ordered him to do so had she known of the situation. Even a merged version of EMIYA with his separate identity preserved was included to serve as a mentor. The reason Merlin said that Artoria had not been told was that several of those timelines had Artoria betray Shirou for reasons beyond her control with lethal results. He chose not to break his King's soul explaining the situation when he already knew what she would have told him to do.
"Silver-tongued devil," Morgan had uttered under her breath. She was unable to refute his points but knew that he had still extracted enjoyment from their collective confusion regardless.
Merlin had gone on to explain that this had an interesting side-effect after Shirou became the Lesser Grail. The weapons in his Reality Marble had stored the data from those various 'bad ends', and the Lesser Grail deemed it relevant information to provide to the relevant Servants summoned thereafter. Hercules starting out with unexpected weapon resistances and Medusa having multiple sets of contradicting memories were both caused by this provided data.
Artoria had allowed her Court Magus to relay his entire story without interjecting. Sadly, he had not proven to her that he deserved forgiveness. "Merlin, I know you as well as any human is able. Do not take me for a fool and claim that doing this and concealing it from me was exclusively for my benefit." Artoria clearly did not believe that Merlin was telling the entire truth in this regard. She knew that the man enjoyed tinkering with things, and there was narrowly restrained anger in her voice at the knowledge that Shirou had been his experiment beyond the scope of what was strictly needed. "Never before have I carried an urge to convey such an...eloquence of rage that would dwarf even Mordred's vocabulary. Only the presence of young ears shields you from the depths of my anger."
Mordred couldn't help but be simultaneously enraged and impressed. Merlin once more had the dubious honor of pulling off the impossible, because King Arthur had never said she wanted to cuss someone out before. It wouldn't be a careless slinging of profanities if she chose to proceed, either. Mordred knew that such crude language from her father would be deployed with all the class and strategic delivery Artoria could muster.
Was it wrong that Mordred desperately wanted to see that happen?
Before Artoria could usher Irisviel, Illya, or Mordred out of the room and make good on her impulse; Merlin and Artemis felt something...bizarre happening with Shirou's Reality Marble. The Clairvoyant looked surprised for once and quickly willed his power to reveal to him the cause of what had just happened, while Artemis used her connection to the Moon Cell to verify the same with its near-omnipotent scans of the Earth. Both reached the same unexpected result.
Merlin finally spoke somewhat tensely into the phone call with Artoria, hiding his relief at being forced to interrupt the previous topic. "I apologize, my King, but your consort's kindness has just drawn some unplanned tag-alongs into his Reality Marble."
Artoria needed a moment to finish collecting herself before responding. "Merlin, his Reality Marble is not even invoked. How might it possibly house intruders?"
"Because your intended has a fascinating habit of doing what should not be possible, especially when he gets it into his head to save someone. This latest development is yet another expression of that ability." Though this result was quite entertaining, Merlin lamented that the boy's timing only gave him a temporary reprieve. The consequences of this might get him in yet more trouble, and Merlin was already in enough trouble as it was.
Artemis gave a giggle. "Don't worry, little Artoria! This just means it's time for me to go in too! I can keep those two in line."
"Wait...'go in'? How?" Vivian inquired just before Artemis placed a hand on the sleeping Artoria's torso and tapped into the power of the scabbard within. Merlin did the same. Both accessed a spell that Merlin had covertly added to the scabbard's interior long ago and began to glow with white light.
"It's an emergency option I added in case I needed to intervene with the boy's inner workings more closely. Pay it no mind, Vivian~" Merlin knew that his words would fall on deaf ears. Vivian and Morgan surely would mind.
"Thanks for everything! We'll talk again sometime! Bye~" The former goddess waved with her free hand before she and the Magus of Flowers vanished in a flash of white energy. The two ladies of the Fae realized that their prisoner had used the link between the two scabbards to bypass the wards of the Garden of Avalon entirely and thus escape his eternal imprisonment...all while in the company of a beautiful woman. Their response disturbed the peace of Avalon for miles around.
"...Meeeerrliiiiiiin!"
Shirou's Reality Marble
Artemis and Merlin arrived in Shirou's Reality Marble and found themselves in the general area of Ryuudou Temple, specifically next to his version of the scabbard at the top of a certain grassy hill. This happened to be within line-of-sight of the Lesser Grail, which was where Shirou had died during Artoria's version of the Fifth Holy Grail War. "Honestly, Lady Artemis...had I not known you were about to employ my emergency intervention spell, I may have been left behind permanently! Those two would not have permitted me to depart from Avalon even to assist Artoria and her suitor. Their hatred of me clouds their reason!" Merlin was slightly irritated at the woman. Artemis responded to his complaints by sticking out her tongue. Saber Artoria, who still listened in over the phone, was silently pondering the implications of Merlin escaping.
"You wouldn't have been much of a Clairvoyant if you didn't see through me right away! Besides, you deserved to be trapped for playing with the hearts of all those women!" Artemis said judgmentally.
The Magus of Flowers simply smiled. "It is quite easy to say that one deserves to be imprisoned forever when someone else is in the cell. Furthermore, the only reason I allowed myself to be caught was to atone for my role in Artoria's fate. The best way I can do that now is by coming here to Shirou's Reality Marble and investigating this matter." Merlin's justifications for his jailbreak were ignored as the Divine Spirit saw the others nearby and called out to them.
"Hey! Don't start without meeee~" Artemis yelled, running over to them and surprising EMIYA quite thoroughly.
"What? Where do you people keep coming from?" EMIYA asked as he dismissed his bow and called forth his married blades, watching the newcomer carefully as she drew near.
Artemis looked at him with blue eyes full of mirth and decided to introduce herself while Merlin strolled over at a more leisurely pace. "Oh, don't be like that! We're both friends of little Artoria! She helped save me and my family when Excalibur and Avalon were first made. I'm Artemis, the Atlantean and Greek Goddess of the Moon! I like romance and things that are sweet, and I hate playboys like Merlin here that toy with the hearts of women! Good boys like Shirou who are chased instead of chasing, though...those stories have their own charm~"
Merlin kept smiling in spite of being introduced in such a displeasing manner, catching up to the group at a more reasonable walking speed. "My, my. Your opinion of me is certainly low, is it not?"
"Wait, you are one of the Twelve Atlanteans? It is wonderful to meet you, Lady Artemis!" Ereshkigal curtsied, clearly remembering her manners in addressing the far more senior deity. Ishtar was also more than a little impressed but attempted not to show it.
EMIYA was becoming irritated and did not share Ereshkigal's respect for decorum. "You still haven't told me why you're all here and how."
"My, how rude of you, EMIYA! You're supposed to introduce yourself to guests. But that's okay! I'll do it for you!" Artemis said, smiling mischievously. EMIYA opened his mouth to stop her, but the excitable woman simply kept talking. "This is EMIYA, a man from a Parallel World's future who gave up everything to protect humans and became a Counter Guardian! Alaya was mean to him and it's made him grumpy, but he's a decent man when he's not trying to push people away or thinking too hard about sad stuff! He was grafted to the soul of his still-living younger self to give the boy a chance of avoiding that fate."
Ishtar and Ereshkigal stared blankly for a moment before the latter took on an expression of pity. EMIYA simply put a hand to his forehead before sliding it over the top of his head in frustration. "Thanks," EMIYA grumbled sarcastically. "Why don't we finally get to how and why you're all here? There was a plan that none of you but Merlin were part of unless he's been hiding even more than I expected."
"What? You dare to imply that I'm unwanted?" Ishtar exclaimed in irritation. "You should be on your knees praying to me for fine women, healthy children, good harvests, and victory over your enemies! Not acting like I am dead weight!"
"But you are dead weight. An Aphrodite knock-off like you might just make things worse...though maybe you'll be alright with the restrictions of childhood imposed on you~" Artemis said in a playful tone, though this failed to conceal the virgin Divine Spirit's disdain for the more carnal and unrestrained aspects of Ishtar's Authority. Ishtar balked at the statement while Artemis continued without pause. "There was a plan, and I am using that plan to advance my own plan! Nothing bad, though. Just something I could never do in a million years if Merlin hadn't made things juuuust right! I jumped over here from the land of Avalon by way of the connection between the scabbards!"
"And just where is 'here'?" Ishtar asked through clenched teeth, her desire to finally get some answers overpowering her rage for the moment. She wouldn't forget the slight against her, though.
"The Reality Marble of an eight-year-old human boy!" Merlin exclaimed happily, knowing what the result would be.
Ereshkigal was confused by the answer, but Ishtar's response was much more...animated. "What? Get us out of here!" The girl visibly panicked, rushing over to the scabbard and trying to force her way into the beam of light surrounding it and lancing up into the sky. She had watched Artemis and Merlin arrive by way of the scabbard and thus considered it the exit. "Let me out! Let me out right now! I don't want my life tied to a mortal's soul! Do you know what would happen to us if he died or if the Reality Marble collapsed? I don't plan on finding out!"
Artemis couldn't help but smile in amusement at Ishtar's response before answering her question. "Assuming the worst? You'd be drawn to the land of Avalon in the Reverse Side of the World along with the rest of us by way of one of several safeguards! No need to panic, Ishtar~" The girl paused her effort of taking aim at the beam of light with her Boat of Heaven and looked back to the amused Artemis. Ereshkigal couldn't help but giggle gently. Merlin simply bore a smug smile. Even EMIYA, the most human of the group and thus beneath her, seemed amused at her loss of composure. Her appearance being that of a child simply made the image worse.
"S-stop that! This is not funny!" Ishtar glared angrily as she floated in front of the beam of light, returning her weapon to its resting position.
Ereshkigal turned her head back toward the visitors, only briefly distracted by her sister's antics before returning to the line of questioning. "My apologies, but I do not understand. How can a Reality Marble manifest in the soul of a human child? I oversaw many souls during my duties and never once encountered such a thing."
EMIYA grimaced slightly before recovering and choosing to be vague in his response. "By breaking that soul at a vulnerable age and cobbling it back together. I don't think you need any more detail than that." Ereshkigal knew better than to accept EMIYA's words as the complete truth but acknowledged that it was his trauma to discuss or reveal. Ishtar gave EMIYA a glare for not being forthcoming but said nothing.
"Thankfully, it isn't something that happens often. A human attaining a Reality Marble during their lifetime has only been recorded happening six times in history," Merlin clarified for the group. "Shirou is the seventh, but he is not yet recorded among their number for good reason. This is a programmable Reality Marble, allowing a great deal of freedom for any Magus' research."
"...you altered a child's soul," Ereshkigal stated in angered realization. It was not a question. Merlin could see that she disliked the idea of tampering with something she considered quite fundamental, which was understandable given her nature as a protector of human souls. Ereshkigal's typically red eyes glowed gold in her anger.
"I restored Shirou's soul to the best of my ability while giving him all the tools I could to survive what may come." Merlin clarified the point as best he could. "Otherwise, he'd either be dead or carry a self-destructive compulsion to save others that would get him killed. Check EMIYA's Reality Marble if you want to see what I started with. I'm confident that you will consider my adjustments to be a marked improvement over the alternative."
"So you used these changes to drag us here and alter us." A suspicious Ishtar accused with narrowed eyes.
"Nope!" Merlin said, almost too happily.
"Wait...'nope'? But you're always to blame for things like this!" Mordred half-shouted over the telephone that was still connected. The voice appearing out of nowhere surprised Ishtar and Ereshkigal, but Merlin simply responded as if it were to be expected.
"Not this time. I can, on this rare occasion, honestly claim complete innocence in this matter." An odd look crossed Merlin's face before he rubbed his chin. "Hm. I had...forgotten what being innocent of an accusation felt like! This is a red-letter day!"
Ereshkigal was not fully satisfied, though a look towards EMIYA to stare into his soul made her nearly flinch in empathy. It was certainly as bad as Merlin had said. Still, she turned back to Merlin and spoke with barely restrained anger. "You will tell me everything about this child's soul. That includes all you have done to taint it and everything you intended to do. Do you understand?" Ishtar was surprised at her sister's vehement response, but it was a reminder that Ereshkigal was no pushover and took her duties seriously. She was a guardian of souls, and it was clear that this one had been en route to the grave when these people got a hold of it. There was certainly a case to be made that this boy's soul fell under her Authority.
"Hmmm...very well. I will have to explain the history between Artoria Pendragon and Shirou Emiya first, to provide some context. I assume you are aware of how Parallel Worlds work?" Merlin checked first to make sure everyone was starting out on the same page. Ereshkigal and Ishtar nodded while Artemis knew she was in for a re-telling of the love story she enjoyed so much. The lattermost didn't want to listen on an empty stomach, though.
"Wait! Before that...EMIYA! It's been too long since I've had human food! Get to work making something sweet!" Artemis demanded in a Taiga-like manner, giving EMIYA little choice but to oblige.
The ex-Counter Guardian supposed that this was marginally better than being enslaved by Alaya.
Copenhagen
Shirou's Reality Marble
115 hours and 9 minutes to Zero
To better facilitate the cooking of a meal and its desserts, EMIYA had directed the group to this Reality Marble's version of the Copenhagen where Shirou had worked in the early-to-mid 2000s. Though more of a pub than an actual restaurant, it was better than dragging trouble to his home.
The destruction that had already been wrought since their arrival had proven him wise.
Merlin was on his third whiteboard by the time food was even served. The first had endured long enough for him to explain the Grail system and most of the Fifth Holy Grail War, but been destroyed by Ishtar when Merlin commented on Gilgamesh's involvement. The second had just been destroyed by Ereshkigal when Merlin explained how he had collected a large number of Shirou's souls from across time and Parallel Worlds, with the aid of a certain bored Second Magician, to merge them together into an extremely strong Shirou with the scabbard Avalon and the sword Caliburn anchored into his very soul. This was along with a massive number of Noble Phantasms stored in his Reality Marble because copying them on sight was apparently a thing his Reality Marble happened to do by default. Saber Artoria, who watched from the World via video call along with the rest of the Einzbern group, maintained her silence.
The revelation that Shirou was heir to First True Magic only for Alaya to try to strip him of his birthright and put a leash on him rubbed EMIYA the wrong way. Ishtar, meanwhile, was envious of someone who could simply create anything he desired. Gems, gold, fine food, Noble Phantasms...this human boy had something even better than an EX-ranked Golden Rule skill.
The Divine Spirits who had shown an irrational hatred for teaching aids were only somewhat placated by the expertly cooked Sumerian meals provided to them. Artemis enjoyed exclusively desserts, though all three were eating ice cream by the end. Only Ereshkigal, who had paced herself as a lady should even in the face of such delights, escaped the ice cream headache.
Looking up from her rocky road ice cream, Ereshkigal was still puzzled. "All of this has been...enlightening, and I must confess that this does seem to be a healthier soul than otherwise possible...but you haven't yet mentioned why Shirou brought me and Ishtar here or why he changed our appearances." Ereshkigal was still curious as to how this could possibly happen.
"That is a somewhat complex question, but I will do my best to answer as concisely as possible." Merlin smiled and drew a large green circle on the whiteboard. "This circle is the Reverse Side of the World." Then, he drew an even larger blue circle around it. "This is the layer that represents the World where humans live. Now, many would say that the Reverse Side of the World is where the rules of the Age of Gods are still in practice and that the World is where the rules of the Age of Man are in practice. They might then tell you that is the entirety of the planet's structure from a magical perspective. However, it is not so simple. There are...layers of sorts that make up these general areas. These are called Textures. While obeying the general rule set of one of the two Sides of the World, they still have their own nuances. A few even obey a mix of the two sets of rules and find themselves between the World and the Reverse Side of the World. Some of these layers can even move about in a manner similar to plate tectonics. Since they can also drift up and down on rare occasions, even breaching the layers above or sinking below them at times, some envision Textures more as bubbles suspended in Imaginary Number Space. It matters not which imagery you use to envision them, so long as the end result is accurate. For example..."
A circle in red was drawn inside the center of the green circle and lazily filled in. "This red circle is the land of Avalon within the Reverse Side of the World, and I filled it in because it is unmoving. It is the heart of Gaia and the core of the Reverse Side of the World where the fairies dwell. Both Shirou and Artoria's scabbards were built and modified here, and draw power directly from it." Then he drew and filled in a black circle within the green circle but outside of the red one. "This black circle represents what was Ereshkigal's domain in the land of Kur, a Texture known as the Sumerian Underworld that sank to the Reverse Side of the World when the Age of Man arrived. Both Avalon and Kur exist in the Reverse Side of the World. However, their rules still differed in that the Land of Kur could only accept the dead and that Ereshkigal normally could not leave. As such, nothing could typically interact with Kur for long periods now that human souls are no longer stored there and Kur was made unnecessary. A vestigial Texture, as it were. Avalon does not have these failings. Even though both are from the Age of Gods, they had rules that rendered them incompatible and were thus separate Textures." Ereshkigal was a bit sad, reminded of her loneliness and uselessness over the millennia, but she shook off the depression to keep listening.
Merlin drew another black circle, but this time outside the green circle and within the blue...though the black circle was not filled in and touched the blue circle's inner edge this time. "An example of a Texture closer to the World's side of things is the Wandering Sea, which appeared in the year 20 AD. A mountain range from the Age of Gods and its surrounding water separated from the World and maintained some of the rules from both the Age of Gods and the Age of Man even as the latter rose to dominance in the rest of the World. Humanity has carefully preserved this texture by regulating the few people who enter it and the beliefs they hold. The belief of the dominant race in a Texture influences the rules within, after all, much like how the humans' belief in Science is causing the diminishing of Magecraft in the wider World and making them generally exist in just one Texture with only a few exceptions. Anyway, this texture moves and typically wanders around the geographic area of the North Sea. It rises every December 31st to breach the outer layer of the World humanity is on and is thus accessible to the larger World, but only for that day before dipping back below into the area between the World and the Reverse Side of the World for the remainder of the year. It's a fascinating topic of study."
"Yeah, yeah. Amazing. What does this have to do with this Shirou boy and his Reality Marble?" Ishtar asked impatiently.
Merlin smiled. "Reality Marbles aren't well understood by modern Magi, but the truth is that they are a form of Texture governed by the soul and beliefs of a single user. They are rejected by Gaia as Phantasms due to their prerequisite Alien Common Sense not aligning with either Age's ruleset and are thus impermanent and costly in energy. However..." Merlin then drew a red circle with a scabbard inside, all also on the inner edge of the blue circle, and a dotted red line leading back to the land of Avalon. "This Reality Marble has a Divine Construct at its core that connects to the land of Avalon in the Reverse Side of the World and confers upon the user its protection. This protection is given by imposing the rules of the land of Avalon on the target to shield it from harm and perpetually restoring it to a 'healthy' state. That has been used as the pearl around which this Reality Marble and its own ruleset has been grafted and grown. It also serves as a power source for the Reality Marble at the same time, so it always remains active."
Ereshkigal's eyes widened in sudden comprehension. "Because the scabbard's protective nature shields the user explicitly by enforcing the ruleset of the land of Avalon, which Gaia would automatically accept, the Reality Marble under the scabbard's protection ceases to be seen as a Phantasm to be culled and is accepted by Gaia! It has minimal energy cost! The scabbard also constantly powers the Reality Marble's manifestation by relaying Gaia's power to it! You turned his Reality Marble into a stable Artificial Texture!"
Merlin smirked as they finally understood. As Rhongomyniad pinned the World to the Reverse Side of the World, Avalon pinned Shirou's Reality Marble to Avalon through slightly adjusted properties. "You've got it! To Gaia, Shirou's Reality Marble has the appearance of a Texture that is both Age of Gods and Age of Man compliant! A 'mid-depth' Texture like the Wandering Sea that lay between the World and its Reverse Side. All he has to do to make it breach the surface of the World is call on it once he learns how to do so. As for its size and detail, that is due to a combination of the large number of souls Shirou has comprising his own, his Mystic Eyes allowing him to process massive amounts of data per soul, the Mystery those souls have collected over 1500 years while stored in the scabbard waiting for rebirth, and the power draw Avalon is offloading from him. The current diameter of this Reality Marble is roughly ten kilometers. More than enough to contain the whole of Fuyuki City and some of the surrounding countryside. I believe he has held back, though. He is capable of containing three Divine Spirits and a Magus of Flowers as well, after all."
"Speaking of that..." Ereshkigal inquired, "you haven't mentioned why I might be here if not to end this...experimentation."
Merlin knelt down and smiled at the pint-size goddess of the underworld. "Well, when all else fails, blame Gilgamesh."
"Gilgamesh? What did he do now?" Ishtar asked in renewed irritation while eating some rainbow road ice cream.
Artemis spoke to the girls between bites of vanilla ice cream with strawberry syrup. "Remember that this boy's Reality Marble is influenced by his soul and his beliefs. For example, he knows I am part of little Artoria's history as well as that of her armaments Avalon and Excalibur. My existence is considered to be a verified fact here, so I am not rejected as a myth like I am by the World. By laying his Mystic Eyes on Gilgamesh and seeing his history, he has come to recognize both of your existences in the same way. Little Shirou later read up on Sumerian legend and of the fight between the two of you in the underworld. It...reminded him of Rin and Sakura fighting at the end of some permutations of the Fifth Holy Grail War and he equated Sakura's suffering to Ereshkigal's. He felt a need to help her, so his Reality Marble subconsciously responded and attempted to extend Ereshkigal a hand. That's just the kind of boy he is~"
Merlin nodded and continued the explanation. "You answered his call. This event even superseded the restrictions imposed on you by your native Kur, which has been weakening for thousands of years. Not only that, but Ishtar is so intrinsically tied to Ereshkigal in all ways that when one is summoned, so is the other. Of course, a Reality Marble could not consume a Texture in most cases. Where a Reality Marble is a transient flicker of power called forth by a warped human soul to briefly emulate a Texture, a true Texture is a piece of the planet's soul that has been rejected by the World over time and shed from the surface to be isolated or recycled. When I modified Shirou's soul using Rhongomyniad as an inspiration, I never expected him to use it in this way. Even my Clairvoyance failed to notice this possibility."
"R-right. Thank you for explaining that. But...what about our bodies, then? Why do we look like this? Is it because he's a child too?" Ereshkigal asked in curiosity.
This time it was Merlin who chose to answer. "Do you both remember what I said of Rin Tohsaka, whose battle with her sister Sakura mirrored your own battle in Kur? That is not the only way in which you are similar. Both of you are so highly compatible with Rin that she could serve as a Pseudo-Servant host body for either of you if the opportunity arose. It is only natural that Shirou would attempt to envision you both using a familiar and compatible form...which happens to be seven years of age right now." Ishtar was about to interject, but Merlin held up his hand so as not to be interrupted. "Fortunately, Shirou's memories also include a seventeen-year-old Rin. Should you focus your energies on changing your age, this place may just oblige you.
Putting down her spoon, Ishtar closed her eyes and decided to try just that. After a few moments of focus, there was a *pop* and a puff of harmless white smoke that dissipated to reveal a seventeen-year-old Ishtar. The transformation was clearly based on something simplistic that an eight-year-old boy would consider fitting, but Ishtar was now confident she could alter that as well in time. She sighed in a mix of relief and irritated resignation. "Well that's just wonderful," she blurted out with heavy sarcasm. "To think our forms and presence are dictated by the whims of a child...Gilgamesh is laughing at me right now. I'm sure of it."
EMIYA smirked at the scantily-clad Divine Spirit. "What, do you find it humbling?"
Ishtar crossed her arms and glared back at EMIYA. "More like infuriating!"
Merlin smirked. "Oh? I would have thought you to be grateful to Shirou as well, Lady Ishtar. Your confrontational conduct in pushing Gilgamesh away from the Sumerian pantheon and sealing their fate was something even your father could not fully protect you from the consequences of. Were you not shunned by your peers and cursed to eternally wear a sign proclaiming you to be a 'useless goddess'? Having a chance at a second childhood to grow up with your sister, something you were initially denied, seems like a far better use of your time."
"Don't even mention that sign!" Ishtar yelled out, blushing in both fury and embarrassment over her failings being revealed. She had thrown that accursed sign away as soon as she arrived in this place and found herself no longer bound to it. The truth of the matter was that Ereshkigal wasn't the only one who had felt the offer of the contract. When Ishtar found herself isolated from her peers, cheated on by that sheep of a husband of hers, and ultimately cast aside to an admittedly lesser degree than her sister; she too had felt the call. A call of concern and pure selflessness that, in her weakness, she had accepted just as her sister had. She was absolutely panicked when she was suddenly plucked from her home and appeared here, so she let Ereshkigal take the blame for their little problem at the first opportunity rather than admitting her own mistake. Ishtar had her pride, after all, and was terrified that the Clairvoyant and the Atlantean would call her out on it. The brunette's thoughts were stopped in their tracks when she saw Ereshkigal looking at her with a certain emotion in her eyes...something which had been absent ever since she started her duties in Kur.
Hope.
In spite of their sometimes lethal sibling rivalry, Ishtar's complaints died on her tongue. She knew how much she had taken her own relative freedom for granted. She knew that her sister had been trapped in Kur for millennia. She knew that Ereshkigal hadn't been given much time with her family to start with. In that moment, empathy that many would not attribute to Ishtar struck with full force and made Ishtar feel like a monster. Her Authority over love included familial love as well, after all.
...maybe being a sister for a change was the right way to go.
With another puff of white smoke, Ishtar was once again in the form of a child. Her arms were crossed and her eyes intentionally avoided looking in Ereshkigal's direction. "W-well. At least I'm not stuck as a child and he called me forth for a proper reason. So long as my contractor provides sufficient offerings of jewels and gold for me, staying here might not be so-" Ishtar was not prepared when a gently crying Ereshkigal suddenly pulled her sister firmly into a full-blown hug. It seemed that the tsundere act was not fooling anyone...so Ishtar allowed an arm to go around Ereshkigal and rub her back in comfort.
Artemis couldn't help but smile at the scene. "Hmm...I think that's a good stopping point. Everyone's heads or hearts are kind of melty right now. Speaking of melty, I want to finish my ice cream while I can~" While the Divine Spirit resumed eating her treat as the sisters hugged, Merlin silently agreed with Artemis that this was a mere stopping point rather than the end of the matter. Oh well, at least he had obeyed his King and told her everything he had contributed. Artemis could take the blame for everything going forward if things got out of hand.
And given the behemoth of metal that he sensed resting beneath the waves offshore, there would probably be a lot of blame to go around sooner or later...
Emiya Residence
114 hours and 58 minutes to Zero
"This is nothing like the archery club at school!" Taiga's complaints echoed in from outside as the Einzberns and Pendragons returned to the living room. It seemed that Atalanta and EMIYA had started an archery lesson for the children outside, currently being attended by Shirou, Sakura, Rin, Gray, and Taiga.
EMIYA spoke promptly in response to the irritated girl who had yet to even use her bow correctly. "Your classmates are probably trained in Kyudo, the Japanese style of Archery. It's taught more for meditation and sport than anything else, though it's still useful for firing arrows while on horseback. Archer and I are teaching forms of Archery from the western world that are better suited for heavier firepower. They're going to be different."
Taiga grumbled. "Of course you'd use something like that mister 'I launch swords at people'."
EMIYA shrugged and gave a smirk. "These techniques kept you alive. I don't care if you're ungrateful, but should you be so immature in front of the kids?"
Taiga sputtered, remembering that she had to look like a reliable older sister type...and given how well Shirou was doing helping the younger kids with their archery, she was already losing! Gray had already learned how to notch the bow with the boy's help! Rin, meanwhile, was looking at the unreliable high-school student with a mix of pity and smugness. At least she and Sakura had learned how to shoot an arrow...even if they had each missed the target completely.
On noticing the return of the Einzbern family, everyone went back indoors and the game on the Sega Saturn was unpaused and resumed. Irisviel and Saber Artoria both felt a need to sit near Shirou after learning just what had been done to him, so Leysritt took over Irisviel's German holdings in the game and started to systematically annihilate Waver's assets in the Baltic with brutal efficiency. Lancer Artoria assisted her, managing Britannia in her Saber self's stead. Saber Artoria, Irisviel, and Kiritsugu all then sat with Atalanta and the children while Rin told the story about how her father took in Shirou and Saber Artoria.
"Your Papa wanted you to marry my brother? Hmph!" Illya commented while crossing her arms. "I'll share him with Saber since she saved him, but that's it! Two wives are enough!" Saber Artoria visibly tensed at the implications. Mordred simply snickered at her father's plight while playing her game.
"W-Wait a second!" Rin exclaimed. "You can't marry your brother! It doesn't work that way!"
Illya shook her head stubbornly while clinging to a confused Shirou's arm. "We're not related by blood, so it's fine!" Shirou had the strangest sense that he'd heard this argument before from the girl in his other life. Kiritsugu had not expected Illya to feel this way and was becoming more than a bit worried. He might have to nip this in the bud somehow.
Sola-Ui, who had awoken and was now speaking with Tokiomi, looked on in puzzlement as Atalanta clumsily tried to explain in vain to Illya why she shouldn't make such a decision so early in life. The red-haired betrothed of Kayneth then spoke on the matter. "Her brother? I thought that Shirou was in your care, Mister Tohsaka."
"He was, temporarily, though there is a bit of an adoption dispute happening at the moment that we've had to put aside for obvious reasons. The destruction of my home has complicated matters further," Tokiomi admitted with a nearly imperceptible sigh. "Both sides are fortunate that we were thoroughly involved before someone from the Norwich or Yggdmillennia families took notice of the boy. Mystic Eyes and that many Magic Circuits aren't easily overlooked when found in an orphan."
Atalanta's eyes narrowed as she turned away from the stubborn Illya to tend to this new information. "So you all want to adopt him because he has magical potential? To use him?" She clearly didn't like what she was hearing.
Kiritsugu refuted that accusation quickly. "No. In the other Parallel World I remember, I adopted him without knowing he had any Magic Circuits at first. I'd even tried to dissuade him from learning Magecraft because of the danger, though that proved to be impossible in the face of his determination. I want my son, my daughter wants her brother, and my wife wants us all to be happy. Even if he had no potential whatsoever as a Magus and had no hope of recovering his memories, our actions would be the same."
Perceiving no deception, Atalanta's expression softened a bit on hearing this before her eyes shifted to Tokiomi for his version of things. The man allowed only a bit of sheepishness to leak through as he spoke. "I will admit to having an initial hope that he would marry one of my daughters and merge his gifts into the Tohsaka family line. In addition, the boy has proven kind, capable, and good to them. Such qualities are rare in the Moonlit World and make finding a truly supportive spouse difficult. Things have changed, though...including my own priorities towards how children should be raised. Sakura suffered because I made a decision from the perspective of a Magus rather than that of a father, and I will not repeat that mistake. This branch of the Einzbern family and I are in agreement that the children would have to make that decision for themselves without pressure when the time comes, though I will not conceal my approval of the boy. He did keep me and my elder daughter alive and has earned the support of the Tohsaka Family regardless of who adopts or marries whom."
This was met with a wary nod from the concerned Servant. "Very well...just remember that marriage is exclusively their decision when the time comes," Atalanta said sternly, accepting their word for the time being.
Irisviel chose then to speak, smiling gratefully towards Atalanta. "Archer, I thank you for defending him, but you needn't worry about us forcing obligations onto Shirou. We don't care about the things that most Magi consider important. Kiritsugu and I just want to give our son a happy childhood full of love!" Irisviel's words and smile were earnest like those of a child, which had an effect on Atalanta's powerful instincts.
Before she could stop herself, the Chaste Huntress had moved her hand and started rubbing the mother's head while smiling warmly. "I don't doubt your intentions, Irisviel. You're a good girl."
"Hn?" Irisviel gently inquired, puzzled by the action. Only then did Atalanta notice what she was doing and hurriedly pulled her hand away as if she had been burned.
"M-my apologies, Irisviel! It was-...you sometimes feel like a child to me. I know that makes little sense..." This was an issue that Atalanta had been dealing with ever since arriving at the Emiya Residence. Irisviel was intelligent, but her feelings and actions were simple and pure like those of a child. It was wreaking havoc on Atalanta's perception of the woman.
"Oh...might it be because my soul is nine years old?" Irisviel asked innocently. Atalanta's eyes widened in surprise, prompting Irisviel to explain further. "Yes, perhaps that is why I seem young to you! I am a homunculus that was created to be sacrificed as the Lesser Grail for this Grail War. I was initially empty of emotion, but Kiritsugu protected me and taught me as much as he could! We fell in love, I had Illya, and the rest is history!"
"You're only nine...you have an eight-year-old daughter...and are meant to be sacrificed?" A horrified Atalanta then gingerly wrapped her arms around the woman and hugged her closely. "I'm sorry I didn't notice, Irisviel. You don't need to worry anymore. Atalanta-nee will take care of everything..." Irisviel was confused by the hug and the promise. She, unlike everyone else in the room, failed to see Atalanta glaring at Kiritsugu as if he were the worst scum alive. Many of the others, including both Artorias, couldn't help but turn their attention towards him as well...
The children, excluding Taiga, were quickly ushered into a different room by Maiya. There was no need to subject them to this sort of conversation.
It took a significant amount of time for Kiritsugu to convince everyone that no, he had not been the one to plot Irisviel's sacrifice; yes, Irisviel had the physical development of an adult from their very first meeting; yes, Irisviel had asked for marriage fully aware of what it entailed; and yes, Irisviel was the one to push for Illya to be conceived. Irisviel assisted in answering these questions, mentioning that she expected to die and wanted to leave Kiritsugu someone to love even after she was gone. They also explained that the functionality of the Lesser Grail had been transferred elsewhere unexpectedly, so Irisviel had a chance of surviving the War.
Being married and having children as soon as one was physically mature enough was far more common in the past and potentially allowed the various Heroic Spirits to accept it a bit more easily, but the idea that Irisviel had gotten pregnant within a year of her own birth was not a popular view for anyone who understood the nature of the problem. This was made extra clear by how Taiga had stood between Kiritsugu and Irisviel with her Torashinai at the ready. Three facts ultimately made the situation tolerable. First was that Kiritsugu and Illyasviel were the only pleasures that Irisviel was permitted to have in the entirety of her life by her grandfather. Second was that Irisviel chose to give birth to Illyasviel as soon as possible so as to have as much time together with her child as she could before her own passing. She admitted that Kiritsugu had actually slowed her down a bit in that regard to ensure that she understood what she was asking for. Third was a point put forward by Mordred when she said "homunculi like us can't always live long enough to reach marrying age anyway."
This statement, while resolving the matter of Kiritsugu and Irisviel's relationship, led to Atalanta bearing a puzzled expression on her face. "...Mordred, please forgive the question, but how old are you?"
"Eh? Well, Mother said I was born on May Day, so..." The young woman did some mental math before giving the result. "I'm eight. Why?" Mordred quickly noted, by way of Atalanta's expression, that her response was perhaps not an ideal one.
Atalanta turned toward Saber Artoria with a furious glare, but saw shame and regret in the blonde King's eyes. That gave her just enough pause to recall the lore of Artoria and Mordred's lives provided by the Grail. Mordred was conceived without Artoria's consent and hid her identity until she had long since become a Knight of the Round. Only the events that happened after Mordred revealed herself and asked for the throne were even partially Artoria's fault. Atalanta sighed and took several moments to calm herself down. "...the guilt for this does not lie with your father. She has freely confessed to what little she is guilty of and is earnestly trying to atone. I must lay the blame almost entirely at the feet of your mother."
"Damn right!" Mordred exclaimed, though the glance of displeasure from her father and the horror on Atalanta's face reminded Mordred to halt her crude tongue. "S-sorry! Still getting used to controlling it, Father. At least the kids aren't here, huh?"
"Wrong, there are still two of them here." Atalanta's words drew Mordred's attention. "Two children who don't even realize how badly they have been wronged. Children who were made to sacrifice their childhoods and ultimately their lives for the ambitions of those who should have loved them." Tokiomi twitched at the intense displeasure in Atalanta's voice and couldn't help but see himself as guilty of such a sin. If he had not already been earnestly repentant for his mistakes by the time she was summoned, Tokiomi suspected that Atalanta may well have killed him herself.
Ryuudou Temple
110 hours and 24 minutes to Zero
Pain. That was the whole of his world on first waking. The left side of his body was in agony, but he couldn't even cry out. Something seized up his vocal cords to deny him even that light reprieve from his suffering.
"Now, now. It wouldn't do to disturb our hosts here, would it?" An ancient old man spoke in quiet tones, but it was clear from his smile that there was ample enjoyment to be found for him in Kayneth's suffering. Kayneth recognized Zouken Matou and wanted to ask what had happened, but still couldn't speak. He raised his head to what limited degree he could and was horrified to see what had become of him. His left side was covered in the mercury of his Mystic Code, Volumen Hydrargyrum, but there was no concealing the severed arm and leg that lay on a blood-stained cloth several meters away. The toxic liquid was taking the form of his missing limbs and covering his wounds and scars, but the half-silver man hardly looked entirely human any longer. "You are fortunate, Lord El-Melloi," Zouken said the title in a manner that indicated little true respect for the station, "that many of your wounds were cauterized by the flames when that house came down around you. The whole left side of your body was mangled and burned...why, you even lost your Magic Crest to the flames."
The horror in Kayneth's eyes was clear. Above the pain and instead of the rage he should have felt, Kayneth El-Melloi Archibald simply felt that all was lost. Tears ran down his face, though they would not wash away the mercury that encapsulated half of it.
"Now, now. None of that, Kayneth." Indeed, Zouken had waited until Kayneth felt the most worthless to cease calling him 'lord'. "You may be a 'powerless cripple who has doomed your family' in the eyes of the Clock Tower, especially since the Tohsaka were not even responsible for the attack on your precious fiancée, but at least I can contribute Crest Worms to give you enough power to sustain your Mystic Code in its new form as your...assistance device."
"Not even...responsible?" Kayneth asked, in horror. The man managed to speak with herculean effort, yet he knew that even this small victory was only because Zouken allowed it.
This was the part Zouken had been looking forward to. "No, the Tohsaka family and Servant had nothing to do with your fiancée's plight. There is a hidden Archer in the War that was responsible for that mess. After you were deemed dead, the branch of the Einzberns that Second Archer was working with formally went rogue and started to consolidate power and allies. The Tohsaka family, the boy, and your fiancée have all been deceived into assisting. Even that ungrateful Waver Velvet has thrown in his lot with them. By assassinating your character and labeling the Grail 'damaged', they have established a coalition to win the war for them. Curse that Magus Killer and his dishonorable conduct..." At Zouken's manipulative words, Kayneth's feelings of inadequacy shifted into a true rage. Yes, this was what Zouken needed to solidify absolute control. The worms in Kayneth's brain were able to seize control of their host more deeply through intense negative emotion or lust, and the control system in Kayneth was far more elaborate and intrusive than the one that had been used with Kariya. After all, the mercury-based mystic code was ideal for the water-based Matou Magecraft to tinker with and control. Mercury tendrils were included in the brain alongside the Crest Worms, strengthening the compulsion on Kayneth to serve the Mystic Code's new master. The spell couldn't even be broken without Kayneth being irrevocably poisoned by the heavy metal.
The five-century-old lich grinned with malicious glee. "You were abandoned, betrayed, and broken...but you can still make your stand so long as I allow it. So, for as long as that battered body of yours holds together, I will have you rage against our foes in my name."
Author's Postscript: Alright, if you've read that massive chunk of exposition and Merlin's attempts at visual aids, thank you for sticking with me. I hope being rewarded with child Ereshkigal and Ishtar eating ice cream helped ease the strain on your minds. The data below is not exactly easy reading, so feel free to ignore it unless you want to know my justifications or have questions.
The following events are canon in my understanding and don't need further justification: the White Titan's attack in BC 12000, the destruction of Atlantis, the defeat of the Twelve Machine Gods, the creation of Excalibur to defeat the White Titan, and the decline of the Age of Gods as a result (the nuances in the flashback chapters ago are my own creation, though). The existence of the World and its Reverse Side is canon. The fact that Rhongomyniad is anchored to the Reverse Side and serves as the linchpin that keeps the World from falling away and exposing the Age of Gods underneath is also canon.
Though not explicitly canon, the ideas that Rhongomyniad is anchored specifically in the land of Avalon and that Avalon is the heart of Gaia as the core of the Reverse Side are both based on both the high energy density and the basic idea that Avalon in canon has the strongest possible protective measures in place against intrusion (exceeding the five True Magics). I feel that this makes Avalon the best possible place for such things to be located. There is also the fact that Rhongomyniad and Avalon come from the same Britannian lore and are far more likely to be related than any other location in the Reverse Side.
The idea that Textures are separated by both distance and Imaginary Number Space is derived from descriptions of Avalon being accessible via the Spiritual Tomb of Albion under the Clock Tower through very specific circumstances(likely including the consent of Gaia or the occupants themselves, otherwise Avalon's barrier would prevent such interaction). Another large hint is that the Atlas Institute was able to develop Paper Moon and Chaldea was able to develop the concept of Zero Sail before Singularities existed and before Lostbelts were even known. They had to get the data to develop these technologies from somewhere, and the closest analogue would be to research Textures. As such, I believe that Imaginary Number Space can be used to navigate Textures, Lostbelts, and (since it was researched for Singularity transit before Chaldea even knew Lostbelts existed), Singularities. Fate/Extra also has Imaginary Number Space and interconnected Reality Marbles in use by the Moon Cell, indicating that Reality Marbles are also traversable with this system. Though there may be differences in application (Reality Marbles not always being active, Singularities having a temporal component, Lostbelts being the overlaying of culled possibilities over the World, etc), this still ties together Textures, Singularities, Lostbelts, and Reality Marbles as having a component of Imaginary Number Space in their location and being traversable through such means. This makes sense because Imaginary Number Space is an additional dimension that exists outside of normal space and time. In addition to x, y, z (3 dimensions of space), and t (time), we have i (an added axis/value that can be used to rotate otherwise identical values or structures to be out of phase with each other in actual physics). An 'imaginary number axis' similar to this was also explicitly used in Prisma Illya by the Kaleidosticks to go to the isolated areas where the Class Cards were; adding even more support for Imaginary Number Space to be the medium by which Textures and other such realities are traversed.
On a side note, it should also be noted that Rayshifting works with both Singularities and Reality Marbles (Final Singularity) and is also likely to work with Lostbelts considering that Chaldea's Rayshifting capability was seen as a threat to the Crypters and was destroyed with extreme prejudice. Rayshifting into Textures would not be surprising in the least given the broad compatibility displayed thus far. I'm still playing through the second part of FGO, so maybe I'll learn more nuances as I proceed.
The larger idea that Textures are a mechanism for removing the Age of Gods from the Age of Man and tend to collect between the World and the Reverse Side is based on several observations and details, but this is an extrapolation rather than canon. The first clue is that what Texture is detailed with significance (Wandering Sea, AD 20) is from within a few decades of a key stage of the Age of Gods transitioning into the Age of Man (AD 0). This is specifically noted to be a place where the Age of Gods is still relevant. It strongly implies that the reason for the Texture departing reality was the accelerating split between the Age of Gods and the Age of Man, but is not conclusive proof. Second is that it took roughly 13,200 years for the process of evacuating Phantasmals and Divine Spirits from the World to the Reverse Side to be completed, measured from the attack of the White Titan to the end of Richard I's reign in AD 1199. This was clearly a gradual process (though accelerated in the AD era) and Textures provide a means for that process to happen in such a manner.
All in all, this isn't something I can explore in-depth without stepping outside the bounds of canon and into the unknown. Still, I'm doing my best to be guided by lore and reason. Thanks for sticking with me through two pages of rambling, and hopefully I have pre-emptively answered some questions.