A/N: For those who might be confused as to why Shirou summoned Artoria, I just couldn't justify a way to get out of it without something happening to Avalon inside of him. So it's still there, and it acted as the catalyst for Artoria.
I do apologize for how long this chapter took. IRL has taken a turn for the strange, but all is looking up again. Back to our irregularly scheduled writing.
The Grail activated like the tolling of a morning bell. Magic poured from the leylines under Fuyuki City and into those who had been chosen as Masters.
A nascent god stirred in the womb, and its shadow raised its head, independent of the being which formed it. A thin rope of black mud slipped from its being, piercing then absorbing a writhing crest worm as it skittered too close to the shadowed being.
The shadow smiled as the darkness rippled away from around its host, and Shinji Matou, pale as death and viewing the world through crimson eyes, stepped out of the basement his grandfather had once used to torment his sister, and into the rest of the Matou home.
Assassin watched him as he left, unblinking as his Lord Master materialized next to him on his perch.
"He is no longer entirely your grandchild, my Lord Master."
Zouken snorted at that, grimacing as he saw the thing wearing Shinji like a suit move towards the kitchen.
"I knew that much already. And it isn't the idiot in control. I suppose it was only a matter of time before he lost control of it. It's more imperative than ever that I get my great-granddaughter back now, then."
It wasn't the greatest situation to be in. It certainly wasn't the worst, but Zouken was the weakest he'd ever been, now that Shinji had been overcome by the shard of the Grail he'd inadvertently stolen from Sakura when he'd killed her. Whatever had been inside of that was in control of him now, and with both of his grandchildren outside of his control, it was only the prana he'd saved up over the centuries keeping him alive now.
Assassin knelt at his side, and began to crumble away into shadow.
"Your will be done, my Lord Master."
Zouken grimaced again. If Assassin failed to get his hands on Honoka, his will was going to start counting for a lot less.
He'd waited for this day for years.
Artoria could tell that much as Shirou began to lay out his preferred tools of war on the table in Rin's workshop in a manner that reminded her uncomfortably of his father.
A map of the city was unrolled next to a physical bow, marked with the most direct paths to his quarry and a few more indirect paths. Pictures of the Matou household were spread above it, depicting areas which might be infiltrated with ease or some effort. Shirou had traded out his daily clothes for the traditional shooting uniform, and had put a strange glove over his right hand.
He was preparing for war, and it left a sour taste in her mouth.
She understood his reasons, and accepted them, even. But as he began to set glass bottles of a sweet-scented liquid on the table, with half-damp rags stuffed in the tops, she couldn't help but find his methods distastefully similar to those of the man that had raised him.
"Master… perhaps this is… a tad overkill?"
Archer burst into laughter on the other side of the table, and immediately winced, grabbing his side as Rin jabbed him in the ribs. She looked at him sternly, before Shirou spoke up.
"Zouken Matou is not a human magus. According to Kotomine, he's legally considered a Dead Apostle, as far as the Church is concerned, and the Mage Association is content to agree, but pretend he's not their problem because he never leaves this city."
He pointed at the glass bottles of gasoline.
"His body is made of Crest Worms, and so long as one of them survives, so does Zouken Matou. And each of them is a living magical circuit. The quality is merely average, but with hundreds of them, if not more, at his disposal, he's the most dangerous Magus in the city. These are just the emergency measures, though."
He spun around her, and opened one of the cabinets behind them to pull out a small suitcase. His thumbs clicked the case open, and he scowled at the contents as he pulled a trio of black cylinders from within.
"These are the main weapons I plan to use against him. Black Keys, courtesy of Kotomine. Conceptualized Scripture bound into the form of a sword. Bastard claimed he gave me a discount because he knew they were for Zouken, and it still cost me an arm and a leg."
Rider glared at Shirou as she covered Honoka's ears, and the father smiled apologetically at his daughter and her Servant.
Artoria frowned.
"And the other one you intend to slay?"
Shirou's hands twitched, and he shook his head.
"The last time we fought, Shinji had some kind of shadow power that could take physical form. Not sure if that was part of what he took from Sakura or something he found in Europe, but… I plan to finish him personally."
Artoria sighed. Her master was an idiot, wasn't he?
"That is foolishness, Master. If his power is reliant on shadows, would it not make sense to save these firebombs for him?"
Shirou shrugged, and slid the Black Keys across the table towards Archer.
"I don't know. Archer, can you Alter these Keys for me? I've never fought someone who had shadow powers before him, and nobody I've met has seen anything similar."
She watched as Archer grinned at Shirou, before incanting his aria and Altering the Black Keys into something else. The blades immediately ejected from where they'd been collapsed, slimming down even further and becoming notched at the back, becoming something vaguely reminiscent of an arrow, if one were seeing it through blinded eyes in the dark and perhaps had no clue how an arrow was meant to look. They had lost none of their potency, however, as Archer slid them back towards Shirou. The younger Emiya nodded his thanks, slipping them into a quiver alongside a handful of thankfully normal arrows. Rin piped up next, prompting the small council's attention to turn to her.
"I called Kuzuki-sensei. Caster is willing to put a Bounded Field around the Matou house to keep the fight contained. She said it should also keep Assassin inside, provided we don't do something drastic like deploy a full-powered Anti-Fortress or Anti-Army Noble Phantasm."
She looked between Shirou and Archer, pointing a finger at both of them in turn. Shirou only blinked at her, and Archer just scratched the back of his head awkwardly.
"Your forward thinking is impressive, Master of Archer, but what did it cost you?"
Now it was Artoria's turn to have a finger pointed at her, Rin's cheeks suddenly flushing.
"I had to listen to those two being all lovey-dovey with one another the entire time! My whole time at high school, and Kuzuki never so much as blinked without a schedule or a stoic look and a monotone! It was disturbing to listen to!"
Shirou grimaced, and Archer winced. Artoria stared at the pair of them, quietly realizing the only physical differences between the two were their hair and eye colors and Archer being just a little bit taller and more muscularly rounded than Shirou; Shirou had the build of an archer who dabbled in swordplay, while Archer had the build of a swordsman who dabbled in archery. They looked like brothers, almost, but there was something in their mannerisms that made them seem like more.
"At any rate, I don't plan to fire anything on that scale. Anti-Thin Wall at the most. I have no plans to die tonight."
Silence fell over the table, and Shirou looked at the map again. He'd committed it to memory long ago. Over the three years he'd been planning his revenge, he'd walked every path to and from the Matou manor, identified as many of the obvious and hidden ways in and out that he could find, and almost certainly put Zouken on his guard with it.
One hand pulled the string back, and the bamboo bent as he tested the draw weight. If he had Archer's proficiency with their shared specialty in Projection, he might have Altered it himself to become heavier. But by that token, he may as well have asked to borrow Archer's own bow, or seen if Berserker could somehow summon his own.
The room started to empty as he set his bow back down. Only Rider, Saber, and Honoka remained with him, and Rider was staring at him intently from behind her blindfold. Saber and Honoka were staring as well, but for entirely separate reasons. Shirou ignored the Servants, instead walking around the table and lifting Honoka from Rider's lap. He pulled her close, taking a moment to steel himself.
"Honoka? Be good for your Aunt Rin and Aunt Ilya, okay? If anyone weird comes near you, I want you to call for Miss Rider. Be a good girl, and know that Papa loves you very much."
He had to close his eyes. It felt too much like a goodbye, and his daughter was shaking in his arms. Shirou sat on the stone floor, rocking her back and forth slowly as Honoka cried herself to sleep.
There were precepts to revenge found in religions across the world.
Kotomine had asked him once, why he sought to fulfill the ancient adage of an eye for an eye. It had been a rare moment of genuine curiosity for the sociopathic priest, and it had left Shirou with much to consider.
He had been so full of fury in the first year. Furious enough that he'd ignored his gut instincts and Rin's warnings that Kotomine was an untrustworthy and unsavory man who espoused philosophies and scriptures he held without any passion or true belief in them, and asked him for training. Of everyone that Shirou had known by the time he buried his wife, only Kuzuki and Kotomine were experienced fighters without peer. The Fujimaru Group had their own fighters, but he'd seen them turn to both of the other men when they had something beyond their understanding to deal with. He'd chosen Kotomine over Kuzuki out of respect for the latter's desire to leave his life's work behind and the knowledge that Kotomine understood him in ways that were simply beyond Kuzuki's ability to comprehend.
He'd eventually been able to answer Kotomine, but it was months after the question had been asked. Why did he want revenge? Sakura wouldn't have wanted him to kill either her brother or grandfather; for all that they'd done to her, she had been content to simply forget them, to let them see her flourish without them and go on with her life. That had been revenge enough for the timid woman. But Shirou wasn't Sakura, and he simply couldn't accept that. His very nature as a sword demanded his enemies pay for their crimes against his family with crimson coins. He was a man who didn't express his emotions, but he felt them all the same.
Shirou laid Honoka in her bed, and pressed a gentle kiss to her forehead as he pulled the blanket over her. Rider stood just inside the door, and though she had her eyes covered with her mask, he found he could feel them watching him as he passed by her. There was only a brief pause as he stood in the doorway, looking back at her with a silent command. Though Shirou wasn't her Master, she nodded, and the man left. In the hall, he was only mildly surprised to see everyone else in the hallway, waiting on him. Rin and Archer, Ilya and Berserker stood by the door, and both pairs watched him pass silently. Kuzuki and Caster followed him when he passed, and at the end of the hallway, Kirei stood, holding his bag of altered sword-arrows. Saber and Gilgamesh stood to the side, the former looking annoyed with her fellow king, who simply stared at her a moment longer before his crimson eyes fell on Shirou.
"So, Shirou Emiya."
Kirei's voice cut through the somber silence of the Tohsaka Manor like a blade. His dull brown eyes lingered on the dull gold of his protoge's own, a hint of excitement and curiosity hiding inside them.
"Do you have an answer for me?"
The younger man nodded, and Gilgamesh perked up, leaving behind his perch on the wall.
"I am not as noble as King Gilgamesh, or as honorable as Saber. I am a sword without a sheathe, and so violence must be done. I want revenge… because it's what I feel like I need to do."
Kirei nodded, a frown of dissatisfaction crossing his lips, and he opened his mouth to speak again.
"So the sword is human after all."
Gilgamesh's words cut off Kotomine's own, and the King of Heroes grinned at Shirou for a moment. Shirou nodded slowly at him, before moving to take his weapons from Kirei.
"Let's go, Saber."
The King of Knights nodded cautiously as her Master began to descend the stairs, following him. Gilgamesh watched as Caster and Kuzuki followed them, and his laughter followed them out of the house.
The Shadow felt it the moment the Bounded Field was erected over the Matou Mansion, and it stirred to life with a grin. It could feel the remains of Shinji's soul screaming as it rose from his bed, garbed in his flesh. The lights in the house flickered and went out as the power lines were severed by magecraft from the Age of The Gods, and it laughed in his voice as it moved. Tormenting Shinji was growing boring, but an old flame had just appeared at the edges of its senses.
It remembered all its last host had known, and knew all this one did as well. It remembered Shirou Emiya, and as it descended the stairs to the front door, it grinned as the Assassin appeared before it. Zouken wasn't far behind, a pile of worms crawling into the old man's shape, his face a writhing mass of frowning abominations.
It might be a sight to behold, the shadow mused, to see three things which were so terribly wrong standing at the entrance hall as they awaited their guest. That was what Emiya and Saber saw when he threw the front doors open, and everything went sideways.
Assassin lunged forward at the same time Saber did, her invisible blade halted by the Old Man's massive right arm. Shirou knocked one of the Altered Black Keys, pulled his bow taut as Reinforcement circuits spread across his body, and the Shadow spun. A tidal wave of inky black surged from Shinji's body, abyssal spears lunging out from the dark waves like a whale breaching the surface, engulfing the entrance hall just as the Black Key was loosed. Arrow met shadow, and the Shadow laughed.
Zouken would have added something to the fight, the aria of a curse forming on his lips, before the sea of dark spears revealed that it was aimed for him. Shinji's eyes glowed with crimson with a malevolent excitement as every worm that made up the being that was the Matou Patriarch, and absorbed them moments before the Black Key sailed through the place his head had been just a moment before. Half a heartbeat has passed, and the Shadow could only laugh as Shirou's eyes came to life with rage as he saw his revenge stolen from him.
There was the other half now. The bow was discarded, and the Master of Saber lunged for the Shadow. The mad cackles of Shinji were echoed by the distorted giggles of Sakura as the Shadow fell apart, sinking into the sea of darkness as Shirou yelled in fury, only to reappear behind the Assassin. Darkness solidified into an obsidian fist, and punched through the Servant's chest, coming out the other side with the Old Man's core in its hand. Tendrils spread across the pulsing thing, and the hand retreated. The core vanished into the ocean at their feet, and Assassin vanished, not turning into motes of luminous spiritrons, but crumbling into smoke that absorbed what little light the moon from the doorway provided.
And then, as Saber landed, he came up behind her. His hand's bindings unclasped and unraveled, the malformed hand that housed the demon Shaitan reaching out for the woman. She spun, batting aside the limb, her Excalibur poised to twist expertly in the air, only for the sea around them to bubble and writhe as spears shot out at her from beneath her. Artoria leapt upwards, gracefully twisting around as she landed so she could keep her eyes on her foes.
"Master, you should retreat."
Her eyes cast towards her master, but the man wasn't listening. His eyes had turned to where the Shadow had absorbed Assassin, standing up as he pulled a pair of Molotovs from his belt.
"No, Saber. This ends tonight, one way or the other."
The Shadow laughed around them, before the form of Sakura rose from the darkness behind Assassin. Shirou froze in his lighting of his firebombs, the crimson eyes staring at him from his wife's face leaving him paralyzed. The Shadow sighed in relief, as if it had simply popped a stiff joint.
"That's so much better. You really should listen to Saber, husband."
It spoke with Sakura's voice now, dancing over its words with malice and drawing out the last word in a mocking fashion. No trace was left of Shinji as it let the shadows dance across its body, coalescing into a dark kimono that reminded Shirou of the one Sakura had worn on their wedding day. His hands shook, gripping the bottle hard enough to send cracks spiderwebbing beneath his whitening fingers. The Shadow could only laugh as the fury in his eyes grew to a bonfire.
"Master, now!"
Saber's words seemed to bounce off the man, who threw aside his weapons and charged towards the Shadow like a Berserker. Its laughter only grew as it weaved under him, and Saber attempted to charge at him, only for Assassin to materialize in front of her.
His arm met her blade as Shirou spun around. A sword Traced in his hands, only for the Shadow to bend itself in half to dodge a decapitating blow.
"So cruel, husband! You would kill your own wife?"
"SHUT UP! HOW DARE YOU WEAR HER FACE!"
The Shadow only laughed again as Saber ducked under one of Assassin's knives, dropping into a spin kick that the fallen Servant easily leapt over. He spun as she did, and Saber had to throw herself to the side as his arm came down. A wall of spikes forced her to turn her roll into a handstand and launch herself into the air. Assassin followed her, a knife batting Excalibur to the side as his hand reached out.
"Zabaniyah."
There was a pulse as his fingertip brushed against her breastplate, a heartbeat that wracked her body with pain, as the Shadow spoke the name of the Old Man's Noble Phantasm through his mask, and Saber screamed in agony. Her heart felt as if it were being shredded apart in her chest, but she hadn't died. Her blade rose-
"EX-"
Prana swirled around the invisible blade, drawing on Shirou's reserves as she aimed at Assassin. The Shadow took advantage of her attack, grabbing onto Shirou by the face, forcing him to look as chains lashed themselves around his arms and throat.
"Watch, husband."
"-CALIBUR!"
There was a flash of bright light, and the Matou Mansion exploded as Excalibur was unleashed inside the building. Assassin vanished moments before the light hit him, and the Shadow laughed again as it commanded the sea of darkness around it to bind Saber as well.
Shirou screamed in fury and pain, struggling against his chains as the Shadow pulled Saber beneath the floor, and the command seals on his hand began to burn away, sending pain shooting through his circuits and nerves.
"Run along now, Shirou Emiya. You've still got two weeks to suffer, and it would be a shame to end it early."
The Shadow heaved, and Saber rose. She had worn blue and silver when she went into the darkness, and had come out in blacks and grays and reds. A gauntlet-clad hand grabbed Shirou by the collar, and threw him towards the street, beyond the border of the bounded field Caster had set up for them. The Shadow curled Sakura's lips into a grin, and leaned into Saber's side as she waved to him before the trio sank into the shadows beneath them and vanished.
Shirou could only watch as they vanished, slamming his fist into the street as he shouted in wordless fury. He ignored the pain in his knuckles, ignored the burning blood that fell from where skin had given way to the sudden union of bone and asphalt. All he could do was kneel there and watch as his plans for the war and his chance at revenge went up in smoke.
A/N: Just in case someone forgot this was the Heaven's Feel route. Hopefully, what happened here was pretty clear, but this version of the Shadow is somewhat different. With it having been absorbed by Shinji, it's less bound by the concept of Sakura's Imaginary Numbers and more by his own concept of Absorption and Parasitism, and then the link to Angra Mainyu gives it the concept of Curse. If we had to treat it as a human, it would have an origin of Curse and an element of Absorption, and I think it's a pretty powerful combination in the hands of a god. As much as I like the original HF's cosmic horror feel, I think the Shadow here should be more personal. Dunno if it and AM are the same thing in canon, but this is fanfiction and thus I can pretend they are, and we get a very spiteful thing that got to see Shirou and Sakura's happy life and learned to fucking hate it, because it was just third wheeling that whole marriage, and so that's why it's changing here. There will be hateboners in Shirou's future.