Hello there! This is Aeon, an Undertale/Persona crossover.

As mentioned, this story works as a sequel of sorts to Overmyth, starting thirty years after the end of that story. However, it may be read as a standalone work, it isn't necessary to read Overmyth to understand the content of this story.

It should also be said this story has some elements from the 'Umineko No Naku Koro Ni' work, however, as no characters or similar elements are in this story, it hasn't been included in the description of the story. All 'Aeon' has from Umineko is the general setting regarding the meta layer of existence, which, although it's a rather important part in the existence of exactly three characters, it's not of great importance in the overall context of the whole story.

The Persona series elements are rather important in the story. Not only it has Shadows, Personas, the Velvet Room and related characters, and twenty-two Social Links, the Persona elements are also the underlying base that makes the story work. Fair warning: although the Personas get introduced in Chapter 2, all that starts taking form in Chapter 10. Please be patient while everything else is set.

Finally, the Undertale elements are the setting and the majority of the characters that take part in this story. As you may suppose, those characters are the ones the Social Links are with.

There should be enough material for exactly 100 chapters, so now you know how long it'll take. There's no schedule for updates. List of characters gets updated depending on who's introduced.

Thank you for reading this note, and please enjoy the story.

How deep is this chasm?

The fact he had been falling for several seconds already meant he was unlikely to survive, but Syphus was feeling frustrated for other reasons. What a chump, he slipped on the wet rocks while traversing Waterfall, lost his balance and fell over the edge of the cliff! In the big scheme of things, this was no more than an inconvenience, but it was a stupid death nonetheless.

At least he had made enough progress in his initial investigation, and had taken the first few steps towards the seemingly impossible task he had. It wasn't all perfect, though, he hadn't understood very well yet how Personas were going to be of help. There was also the matter of the three Social Links he had started, and those seemed to be of even less help towards completing the goal, and what a goal it was!

How was he supposed to find a way to break the Barrier without using not even a single human SOUL?

Before Syphus could wonder what his next step could be, he crashed against the water, the impact breaking his neck and killing him instantly.

-ooooo-

Prologue: Setting Up the Board

Nine hours earlier

Sisyphus ran through the halls of the mansion, holding his glasses in place while hurrying towards the tea parlor. Outside the windows, purple clouds and mist whirled everywhere, the usual landscape in this plane of existence. Not that he knew much about what was beyond the manor, he hadn't been outside since he had been taken there thirty years before. Lucia, the witch who had taken him in, had asked him to go to the tea parlor, where she said there was something of the utmost importance to talk about.

"I'm sorry I'm late, I had to—?" Sisyphus' excuses, said as soon as he opened the double doors to the parlor, were quickly forgotten once he realized the strange environment he was looking at. The noise of pistons and steam, the cogs lining the walls, and the blue metallic coating of the floor and walls made the room resemble a machinery control room instead of the luxurious parlor that used to be behind those doors.

There were people inside the room. Across a large table and sitting on a large blue couch, there was a man with a rather long nose. Bulging eyes evaluated Sisyphus' confused stare, chuckling to himself. To his side, on a separate armchair, there was a young person wearing dark blue coveralls, with short white hair and yellow eyes, looking at Sisyphus' baffled face with restrained amusement. "...what's this...?" Sisyphus mumbled.

"Welcome to the Velvet Room" the man with the long nose said, beckoning Sisyphus towards the empty chair in front of the table. "My name is Igor. I'm delighted to make your acquaintance"

"The Velvet Room? What's this place...?" Sisyphus started approaching cautiously, ready to bolt at the first sign of danger "Where's Lucia?" he inquired, glancing around before sitting down. The androgynous assistant averted their eyes away.

Igor ignored the last question, instead focusing on the first two: "This place exists between dream and reality, mind and matter…

Only those who have signed or will sign a contract may enter…please, take a look at this" Igor extended a piece of paper towards Sisyphus, who took it and started reading it all. There was only one single line of text, and underneath it, a dotted line to sign.

"I chooseth this fate of mine own free will."

So that was the so-called contract...that seemed like a simple demand. "What's the catch?"

"The only thing we ask for is that you abide by this contract, and take full responsibility of any choice you may make during your journey" Igor stated, pushing a pen towards Sisyphus. After a moment of hesitation, Sisyphus decided to sign, after all, wasn't taking responsibility for one's actions something everyone should be used to? It seemed like an easy condition, although part of himself felt like an idiot for signing a contract a stranger he just met gave him.

Igor's grin seemed to widen a bit when Sisyphus gave back the contract with his signature. "Splendid"

"Now what?" Sisyphus asked, looking around the Velvet Room he apparently had a right to enter to now. Now that he was taking a better look, he noticed that around half of the cogs lining the walls weren't moving, despite seemingly forming part of the same machinery. It made no sense for so many cogs to not to be active. Noticing Sisyphus' interest in the quirks of the Velvet Room, Igor's assistant spoke:

"The Velvet Room's state could be considered an extension of the guest's subconscious. What you see is based in you" Sisyphus thought he understood what the attendant meant with that, but he didn't ask for confirmation.

Since the attendant had talked, Igor decided this was a good moment to introduce them "This is my assistant" Igor gestured at the androgynous person to the left with a flourish of his hand. The assistant, noting it was their turn to present themselves, nodded and bowed their head.

"My name is Alphonse. My task will be to aid you in your journey" Despite the name, Sisyphus couldn't say with certainty Alphonse was a man.

"...hello" Sisyphus adjusted his glasses, a bit uncomfortable at the way Alphonse stared at him without blinking. That person had an air of familiarity that seemed inviting, but their piercing gaze and unflinching demeanor made Sisyphus rather nervous.

Having introduced his assistant, Igor continued with the usual introduction to the Velvet Room. "From now on you'll be considered a guest of the Velvet Room. You may be wondering why you're here in the first place" he said, eliciting a curt nod from Sisyphus "In the immediate future you'll find yourself burdened with a task that may seem impossible. However, the fate of not only you, but also of many other people, relies on you accomplishing that goal. It's imperative you succeed, or many people's futures may be forever lost"

Fantastic. So now he was responsible for who knows how many people's futures. ...I really didn't come prepared for this. Perhaps suspecting the new guest was starting to feel trepidation, Igor added: "Alphonse and I will aid you in the completion of your goal, as you'll find our services will prove essential for your success. We'll settle the details of your power at a later point"

"I'll get in contact with you in an hour" Alphonse clarified.

"If you leave through the door you entered through you'll return to the manor you came from. Please take this time to reflect on what your fate will bring you, and what you may learn from it. Until then, farewell" Igor's tone made clear there was no reason to talk any further, as it was unlikely Sisyphus would receive any of the answers he sought. Alphonse didn't seem willing to be any more cooperative, either, so Sisyphus slowly went back through the double doors, closing them behind him and staring at the wall in disbelief.

"...alright, what was that?" he muttered. During his thirty years living in this layer of existence he had never experienced or even heard of people like Igor and Alphonse, and the fact the meeting had led to signing a contract made Sisyphus a bit nervous. He'd be responsible for all the consequences that would come from his actions? What would he do? What consequences would there be? And why had he been so suddenly burdened with the fates of a bunch of people he didn't even know about? Shaking his head as if that was going to clear up the fog in his head, Sisyphus opened the double doors again.

This time behind the doors there was the place he was supposed to go to in the first place: the tea parlor. There was a blindfolded woman wearing a Victorian dress and sitting in front of a large hexagonal table, tapping her fingers against the armrests of her chair. She looked like a soft-spoken and calm person, but more often than not she defied such appearance "About time you got here! What took you so long?"

"...I don't know. To be honest, I don't know" Sisyphus replied, sitting to the woman's side. That was Lucia, his mentor. Thirty years before she had "saved" him from being eternally banished from his home universe, and claimed to have turned him into the same thing she was: a witch. She usually treated him more like a servant, though.

"Fine, let's not focus on the details. What matters is that you're here and I won't be talking to the air anymore" she reclined on her chair "How have you been progressing with that hobby of yours?"

Sisyphus grit his teeth, but stayed respectful. "It's not a hobby, it's a serious matter" The universe Sisyphus had come from was under study by the apprentice, as he was trying to find out the best future possible for the inhabitants in that world. He had spent forty-six years on it already, and all he had managed to do so far was make a few things worse than they were before. Lucia knew that very well, and seeing her take it so flippantly irked Sisyphus, although he tried not to give her the satisfaction of seeing it.

Judging by the way she was smirking, she knew she had annoyed him. "Rejoice! I have decided to lend you a hand. As the Witch of Hope and your teacher, it's only appropriate I give you a tip"

And it took you thirty years! Thank you, oh graceful teacher. Sisyphus gave his best false smile "Thank you, but what kind of tip is it?"

"You're going to love it" Lucia moved her hand over the table. On the surface a large object appeared. It was a very ornate chessboard, almost covering the whole table, with big and intricate pieces lined on the edges of the board. The side with the white pieces faced Sisyphus, while the other side faced no one. Sisyphus stared at the board, knowing what it was, but waited for Lucia to say more about it. She loved to speak without interruptions. "How about you stop doing things from a distance and take a more...hands-on approach?"

"Through a game? You created this fragment?"

"Yeah. Doing things your way didn't work. Enough tweaking with the timelines, that's for chumps" Lucia grabbed the white king piece "Let's give it a try my way. It's nothing you haven't seen before, it's the usual antagonist side creating problems, and the other side having to solve them. It should be entertaining"

If it was 'entertaining' for a witch, then it meant it'd be a major disaster for whatever world they were going to meddle with. Sisyphus felt a pang of pity, what kind of adventure had she crafted now? The fact she was messing with the universe she had come from, possibly playing with the fates of people Sisyphus once knew, made him feel a weight in the pit of his stomach. With some luck it wouldn't involve murders, like usual. Sisyphus swallowed nervously, this didn't bode well. "And how is this going to help me create the perfect timeline I have been trying to create, exactly?" Lucia's eyes flickered to the board and back to Sisyphus, the message was clear: win. "Oh".

They're all screwed.

At least, by taking his spot as one of the witches playing, it'd mean he could do some damage control. "Okay, I accept. Let's do it"

Lucia put her chin on her hand. "Don't jump into the fray like that, Sisyphus. There are a couple things you should know; this won't be a normal game. First than all: I won't be your opponent"

"Wait, what?" If Lucia wasn't going to be Sisyphus' opponent, who would it be? He literally didn't know anyone else who could be, no other witch had ever visited the Hopeful Star manor during the thirty years he had lived there! "Then who...?"

"You don't know him. He's a sorcerer too, that's all you should know right now" Lucia tapped the surface of the board distractedly "He should arrive in a couple hours"

So not only the game was going to mess with all those lives and create who knew what sort of trouble, but also Sisyphus was going to fight against a complete enigma. This wasn't encouraging at all, but by now it was too late to back off. If he did, chances were that Lucia would be the one to play on his behalf. Confirmed, I have to play. "And what's the second thing I should know?"

"You're going to be inside the game"

Sisyphus stared for a moment, caught off-guard. "W-What?!"

"You're going to take active part in this game! Don't think about it too hard, just do what I tell you and all should be fine" Lucia shrugged "It'll be like going back home, won't it? You'll finally be back inside the same universe you came from" after a short pause, she added: "I thought you'd be happier about that"

Sisyphus had never expected to be allowed back into reality, not even as a piece. His body had been destroyed and his SOUL mangled, it couldn't be that simple! What did Lucia and whoever the other sorcerer was do to the fragment or timeline this board represented? "...I-I see...and how do I win? What is the win condition?"

Lucia's expression turned absolutely serious, Sisyphus could feel her intense stare from behind the blindfold. "You'll have to find a way to shatter the Barrier without using human SOULs" she said "I'm not saying you or your piece have to do it. In my opinion, it'd be easier if you found a way and then made someone else do it. Do whatever you want. What's important is that the Barrier must be destroyed without using those SOULs"

Something in Sisyphus' expression must have changed because Lucia leaned forward, eyeing him with concern. So that was the goal Igor had been talking about! And he had been right, it sounded impossible. Not even with his magic skill as the budding Sorcerer of Hope he would be able to shatter the Barrier. Someone of Lucia's age and skill may be able to do it, but there was no way she'd help. How was he supposed to make sure such outrageous feat happened, then?

Refusing wasn't an option, though. It was bad enough that Igor had stated the fates of an unknown amount of people depended on him, now he understood those people were the people from the world he had come from. There was no way he could refuse.

"...h-how do I start doing this? If my opponent will arrive in a couple hours, then what should we do right now?"

Lucia, looking rather amused, nodded slowly. "How about you get the upper hand now? Let's take a look at the board before our opponent arrives. And for that, you're going to need a piece..."

-ooooo-

The man groaned, keeping his eyes closed and grabbing his head. Sudden pangs of pain made his head pulse, it was a rather nasty sensation that got him disoriented and feel rather weak. Shivers ran down his back despite how warm it was in whatever place he was in, he felt nausea and swayed as if he was about to faint. After making sure he wasn't going to throw up or have an attack of panic, the man let go of his head and opened his eyes.

He was sitting against a purple stone wall, leaning against what looked like a small pool of ink sticking to the wall and to the back of his beige field jacket. The room he was in right now was almost empty, there were a few vines on the walls, and a couple switches on the floor. A path of a lighter purple color crossed the room, passing through a dark doorway that led towards who knew where. Feeling how his legs were trembling, the man stood up and slowly walked towards the switches on the floor, pressing them. Nothing happened. Maybe whatever mechanism it triggered was deactivated? That thought made the man's head hurt again, so he stopped and leaned against the wall. This room seemed vaguely familiar, but where...? Alright, try to remember...

My name is...Syphus, and I am...I'm a piece. The thought came to mind immediately, that was the most basic fact. Somehow, the thought he was more like a higher being's limb didn't seem as awful or distressing as it would be to other people. That was his role in the story, there was no need to waste time denying what he had been created for. Syphus closed his eyes, leaning on the wall. My master placed me in the...I'm in the Underground. Did I appear out of thin air or something? I don't remember a thing...? Syphus literally had no memories about a past life. As far as he knew, one moment he didn't exist, the next he was right there in this purple room.

It didn't take long for him to remember everything else: his mission – if I'm a human being with no magic or amazing skills then how am I supposed to destroy the Barrier? – and, right after that, a lot of information about the Underground. It seemed Syphus' master was rather knowledgeable about the places and workings of the Underground, many of its people and about events that happen in countless other timelines. All this information was supposed to be vital tools to know what to do, but he felt a lot of nervousness at the perspective of having to be in a place as potentially hostile as the Underground.

Although he was a bit scared, staying in this purple stone room forever wouldn't help achieve the goal, so going outside was the only option. Syphus peered through the doorway, being careful not to make any noise in case there were monsters nearby. The next room was empty too, so Syphus crossed the doorway and tripped with something that was on the floor. Syphus managed to grab onto the wall and looked at the object: it was a wooden box. A bit puzzled, Syphus opened the box, looking inside. There were three objects and a note, which Syphus took and extended.

You're going to need help.

-Lucia and Sisyphus

...right. Syphus recognized his master and that other witch's names, it was good to know that they weren't just going to throw him into the deep end of the pool just like that. A bit relieved, Syphus took one of the objects given to him.

It was a brooch, flat and seemingly made of stained glass. It was a firefly, blue and rather detailed. While the brooch was a beautiful trinket, how was it going to be of help? Maybe I can obtain a good amount of money selling it he thought, pinning it on his field jacket. While he was doing it, his fingers pressed onto the firefly's head, which caused his body to flicker, as if static had suddenly covered it. "W-Woah!" he jumped back, staring at his hands right before what he was seeing drastically changed.

His hands were now covered in moss green scales, and conical black claws had sprouted from fingers as short and thick as clubs. "What the hell did just happen?!" Those didn't seem to be the only change, though. All over his arms, the back of his head and seemingly extending down his back and legs, there were lots and lots of long white feathers. As soon as he noticed that the feathers bristled, and he also noticed he had some sort of snout, resembling a snake's. Syphus tried to grab his snout, as if trying to convince it was real, but his hands went through the it as if it was no more than air. "...whaaaat?" he muttered, trying to grab it again, but there was nothing tangible there. A quick inspection of his claws and feathers confirmed he couldn't grab those either. Okay, I didn't suddenly mutate into a monster. This is no more than an illusion... That was a better thing than having his body changed like that, and overall this was a positive thing! After making sure he was able to deactivate the illusion by once again pressing on the brooch, he sighed in relief.

You obtained Firefly Brooch

This'll make easier to not to get anyone's attention but it'd be great if I didn't look like a badly plucked chicken! Oh well. As long as no one touches me I'll be okay. How he'd make no one touch him was something he'd deal with later. Syphus activated the illusion again, and took out the second object.

It was an axe blade of some sort, with a short spike on top. The blade and the spike were so dull he could press against those without getting hurt. When Syphus took it, a wooden bamboo handle came out of the end of the blade. A halberd? What do I need a halberd for? The thought of having to fight monsters wasn't pleasant.

You obtained Compactable Halberd

Syphus grabbed the handle of the pole weapon, finding it rather flimsy. As a weapon this halberd was a bad one, and it was more likely he would hurt himself than a foe. Syphus retracted the pole back onto head of the halberd, tucking the weapon into his jacket. Better not to walk around with such thing on sight, even though the weight of the halberd was awkward and unwieldy.

The last item was way more mundane, just a bag with 100 gold coins. As Syphus didn't know if it'd be possible for him to obtain gold at any point, this was a welcome gift. And 100 gold should last a while, shouldn't it? At least he hoped, or things would get complicated for him.

Syphus made his knuckles crack, made sure the illusion Lucia had provided him was working, and walked into the depths of the only passage there was. He had no idea how to achieve the task he had been burdened with, but he was willing to give it a serious try...

...and if Lucia and the other sorcerer had created this game then there must be some sort of twist. As a first step, it would be a good idea to obtain information. Maybe checking the Barrier itself was an intelligent decision, too? There was no guarantee he'd be able to get all the way there, but during the trek to the castle in New Home he would be able to see if there were any anomalies anywhere.

What kind of changes could there be in this timeline compared to all others? What exactly the Velvet Room had to do with any of this? Syphus could feel there was something bigger behind scenes, something he didn't understand yet, and although the thought of being no more than a piece more in the maelstrom of events that was likely to happen during the next few days gave him some dread, at the same time he felt sort of excited.

Let's get this started.