Chapter Text
The basement room of Tokyo Jujutsu High smelled of damp concrete, stale tatami, and the distinctly sharp aroma of cheap pork bone broth.
Itadori Yuji sat cross-legged on the floor, a plastic fork balanced carefully between his teeth, staring blankly at the flickering television screen. Gojo had left three hours ago after dropping off a stack of DVDs that ranged from eighties action flicks to questionable low-budget horror, leaving Yuji with explicit instructions to "keep his cursed energy steady" while watching a protagonist get chased by a man with a chainsaw.
The problem was not the chainsaw. The problem was the voice currently echoing through the back of his teeth like a tuning fork struck against iron.
"You are slurping," Sukuna growled. The sound didn't come from the room; it vibrated through Yuji’s mandible, making his molars ache. "Stop slurping. It is irritating."
"It’s ramen," Yuji muttered around the fork, not bothering to take it out of his mouth. "You’re supposed to slurp it. It cools the noodles down."
"I do not care about your temperature regulations, brat. You are inside my domain of consciousness, and every wet, disgusting sound you make echoes across the water. If I had my full body, I would strip the flesh from your ears."
"Yeah, yeah. You said that yesterday about the potato chips." Yuji set the plastic cup down on the low table, wiping his mouth with the back of his forearm. He leaned forward, resting his elbows on his knees, and looked down at his own hand. "Look, Sukuna. We gotta talk about this. Gojo-sensei says I need to get better at controlling my emotions so I don't bleed cursed energy everywhere, but it's hard to focus when you're screaming at me every time I eat."
A mouth tore open on the back of Yuji’s right hand, sharp white teeth curling into a vicious, mocking sneer. Red eyes blinked open on his cheekbone, casting a faint, crimson glow across his nose.
"I do not negotiate with flesh," Sukuna sneered, his tongue flickering against Yuji's knuckles. "You are a cage. A dull, loud, intolerable cage. You exist to carry me until I decide to break you."
"Right, but until then, we live together," Yuji said, completely unfazed. He had been dead once; his tolerance for ancient evil entities had drastically shifted since June. "So we make a rule. A deal. Like one of those Binding Vows you talked about when you brought me back."
Sukuna’s mouth let out a sharp, barking laugh that rattled Yuji’s wrist bones. "A Binding Vow? You don't even understand the basic principles of cursed energy, brat. You would accidentally vow away your tongue."
"I’m not stupid!" Yuji protested, sitting up straight. "It’s simple. A vow is just a promise with magic back-up, right? You promise not to bug me when I’m trying to relax or do stuff, and I promise... I don't know, to give you control for five minutes when we find a really good meat shop."
The red eye on Yuji’s cheek narrowed slightly. Inside the dark, watery expanse of the Innate Domain, sitting atop his throne of dried bone, Sukuna leaned his chin into his palm.
A vow proposed by an ignorant child, Sukuna thought, a slow, cruel spark of amusement lighting up his mind. He understands nothing of conditions, penalties, or wordings. I could frame this so broadly that his very soul becomes subservient to my intent without him realizing it until the contract snaps shut.
"Fine," Sukuna’s voice reverberated from Yuji’s cheek, unnaturally smooth, dripping with deceitful condescension. "If you wish to draft a pact, brat, we shall draft one. But we use proper terms. No 'meat shops'."
"Okay," Yuji said, nodding earnestly. He leaned over to grab a notepad and a chewed-up ballpoint pen from his school bag. "What are the rules?"
"First," Sukuna began, his voice dropping an octave, carrying the heavy, ancient resonance of a ritual, "Neither party shall inflict permanent physical harm upon the core of the other's soul during the duration of this arrangement."
"So no cutting my arms off from the inside?" Yuji clarified, pen hovering over the paper.
"Precisely," Sukuna purred. Standard non-aggression. Harmless. "Second: Should the vessel experience a state of severe internal disturbance—distress, agitation, or spiritual instability—the King of Curses shall manifest to stabilize the vessel's immediate environment, ensuring the vessel remains fully intact and functional."
Yuji blinked. "Wait, so if I'm stressed out, you help me?"
"It ensures my housing remains undamaged," Sukuna lied smoothly.
In reality, Sukuna had worded it so that any time Yuji felt extreme panic—say, during a execution attempt by the Jujutsu High elders—Sukuna would be forced by the vow to manifest and obliterate whatever was causing the stress, effectively giving Sukuna total permission to butcher anyone threatening Yuji without Yuji being able to suppress him. It was a masterpiece of manipulative framing.
"That... actually sounds pretty nice of you," Yuji said, scratching his head with the butt of the pen. "Okay, what about the penalty if one of us breaks it?"
"The party in breach shall suffer a complete seal of their cursed energy for a period of twenty-four hours," Sukuna declared.
To Sukuna, this was zero risk. Yuji didn't even know how to intentionally break a vow, and Sukuna had structured the terms so that he himself was doing nothing more than promising to defend his own container. It was foolproof.
"Alright!" Yuji grinned, slamming his hand down on his knee. "I agree! No hurting each other, you help out when I'm feeling awful, and if either of us mess it up, no magic for a day!"
"Then swear it," Sukuna commanded, the eye on Yuji's cheek curving into a sinister crescent. "Say: 'I accept these terms under the canopy of the soul'."
"I accept these terms under the canopy of the soul!" Yuji shouted cheerfully.
For a second, nothing happened.
Then, a sudden, suffocating weight dropped onto the room. The air turned cold, heavy with the smell of ozone and old blood. A thin, black line of ink-like cursed energy coiled around Yuji’s wrist, sinking deep into his skin before vanishing into his pulse point. Inside the domain, a similar mark burned itself onto the pillar behind Sukuna’s throne.
The Binding Vow was set.
Sukuna let out a low, victorious dark chuckle. Foolish boy. You have just given me carte blanche to step in whenever you fear for your life, completely bypassing your will—
THUMP.
Sukuna’s train of thought was violently derailed as a terrifying, agonizing force yanked his spiritual form straight out of the skull-throne.
In the real world, Yuji didn't even have time to blink before a sudden blast of black and red smoke erupted from his shoulder. When the smoke cleared, Sukuna’s upper torso was fully manifested—not as a tiny mouth on Yuji's skin, but as a solid, physical entity sprouting directly out of Yuji’s left side like a grotesque, four-eyed Siamese twin.
Yuji yelled, jumping backward, which only caused Sukuna’s physical weight to drag them both sideways into a pile of laundry.
"WHAT THE HECK?!" Yuji screamed, scrambling to sit up. "Why are you out?! Did you break it already?!"
Sukuna was staring at his own four arms—two of which were currently pressed against the floor to keep himself from tumbling off Yuji's body. His eyes were wide, the crimson irises vibrating with an unholy mix of rage and absolute, utter bewilderment.
"What... did you do?" Sukuna’s voice wasn't echoing inside Yuji's head anymore; it was booming directly into Yuji’s left ear canal, loud enough to cause a faint ringing sound.
"I didn't do anything!" Yuji yelled, trying to push Sukuna’s massive, tattoo-covered chest away from his shoulder, only for his hand to slip on Sukuna's smooth, physical skin. "You said 'distress'! You said if I was distressed, you’d show up!"
"I said severe internal disturbance!" Sukuna snarled, his lower set of arms reaching out to grab Yuji by the front of his hoodie, lifting the boy off the floor. "I meant life-threatening combat! Spiritual collapse! Fatal trauma!"
"Well, I was watching the movie!" Yuji gestured wildly toward the TV screen with his free hand, where a low-budget zombie was currently jump-scaring a teenager. "The guy with the chainsaw showed up right when we made the deal! It gave me a heart attack! My heart rate went up!"
Sukuna froze.
Slowly, agonizingly, the ancient King of Curses turned his head to look at the small, outdated television set. On the screen, a poorly rendered monster roared.
Yuji’s heart was pounding against his ribs—a steady, fast thump-thump-thump of mundane, teenage jump-scare anxiety.
The Binding Vow, utterly unconcerned with literary intent or grand ancient evil, had interpreted 'vessel experiences emotional distress' in the most literal, unrefined way possible. Yuji was startled by a cheap movie; therefore, the Vow had compelled Sukuna to physically manifest to "stabilize the environment."
Sukuna tried to force himself back into the domain. He concentrated his immense will, commanding his spirit to retract beneath the skin.
Nothing happened.
A sharp, searing pain shot through Sukuna’s chest—the Vow enforcing its binding terms. If he tried to force his way back in while the "distress" condition was active, it would trigger the breach penalty and lock his cursed energy for twenty-four hours.
"You..." Sukuna’s voice trembled with a rage so ancient and dense it made the floorboards groan. "You absolute, brainless, pathetic little worm."
"Hey! Don't yell at me, you wrote the vow!" Yuji snapped back, though he was still awkwardly bent sideways because Sukuna’s weight was heavily off-balancing him. "Can you at least put me down? You're heavy!"
"I am the King of Curses!" Sukuna roared, his extra pair of eyes flaring blindingly red. "I do not get dragged out of my domain because a fictional peasant got eaten by a puppet!"
"Okay, well, tell that to the magic wrist ink!" Yuji reached over and tried to turn the TV off with the remote, but Sukuna’s top left hand instantly shot out, snatching the remote from Yuji's fingers and crushing it into fine plastic dust.
"Aw, man! Gojo-sensei's gonna make me pay for that!"
"Silence!" Sukuna hissed. He closed all four of his eyes, taking a single, deep, incredibly furious breath. His massive, muscular frame flexed, pulling Yuji’s shoulder along with it. "Calm down, brat. Lower your pulse. Immediately."
"I can't lower it when you're screaming at me and popping out of my body like a weird jack-in-the-box!" Yuji yelled back, his face turning red from the strain of holding up Sukuna's extra torso. "Just relax! Take a breath! Think about... ocean waves or something!"
"If you speak to me of ocean waves again, I will flay your skin and make a sail out of it," Sukuna threatened smoothly, though his voice lacked its usual grandiosity given that he was currently tethered to a high schooler wearing sweatpants.
For three agonizing minutes, they sat on the basement floor in dead silence.
Sukuna remained half-manifested, a monstrous, terrifying deity sprouting out of the side of an athletic fifteen-year-old. Yuji closed his eyes, concentrating furiously on breathing in for four seconds, holding it for four seconds, and breathing out for four seconds, just like his middle school track coach had taught him.
Slowly, Yuji’s heart rate settled. The jump-scare faded. The ambient stress receded back to its normal baseline of 'mildly confused about geometry homework.'
With a soft shhhk sound, the magical tension released. Sukuna’s physical form dissolved into a cloud of red-and-black mist, sinking back down beneath Yuji's collarbone until only the thin, black tattoos remained on Yuji's skin.
Yuji let out a massive sigh of relief, flopping backward onto the floor, staring up at the concrete ceiling. "Man... that was intense. Binding Vows are no joke."
Inside the domain, Sukuna sat on his throne of bone, his head resting in both of his upper hands, his lower set of hands clenched into tight fists.
He was trapped. He was legally, spiritually bound to a boy whose stress responses were triggered by bad horror films, pop quizzes, and probably late-night cravings for convenience store meals.
"Itadori Yuji," Sukuna’s voice drifted up from Yuji's chest, cold, deadly, and entirely devoid of joy.
"Yeah?"
"If you ever feel distressed again... I will personally ensure that whatever caused it suffers a death so terrifying that the gods themselves will weep."
Yuji sat up, scratching his chin. "Does that include when the convenience store runs out of the strawberry milk I like?"
Sukuna didn't answer. The silence from the Innate Domain was absolute, radiating a cold, dark promises of future violence.
Yuji just shrugged, reaching over to pick up his bowl of lukewarm ramen. "Guess we'll find out tomorrow."