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The family sin

Summary:

Fifteen-year-old Yuuji Itadori lives an idyllic teenage life split between school, track training, and his friends. Everything changes in a single evening when Sukuna—Jin’s twin brother and a ruthless ex-convict fresh out —steps into their home. A single glance at his nephew’s pure, blossoming youth awakens a dark, incestuous fixation within Sukuna.

Notes:

I wanted to write a Sukuna x Yuuji AU story

Chapter Text

 

The light in the Itadori family kitchen had that warm, muted glow that made everything in the house feel safe. Jin Itadori stood by the stove, softly humming an old tune as he stirred the dinner sauce. 

 

A fresh loaf of homemade bread, baked right after work, already sat on the table. For Jin, this small ritual of cooking and maintaining the home was the only way to keep a semblance of normalcy after years spent in silence, raising his son entirely on his own.

 

And then, the front door slammed shut with a loud, cheerful bang.

"Dad! It smells amazing all the way from the street!"

 

Yuuji practically burst into the hallway, his school bag hanging over one shoulder and sports gear in his other hand. His face was flushed from running, his hair slightly tossed by the wind, and that trademark, wide grin was plastered across his lips. 

 

At fifteen years old, Yuuji was the embodiment of pure, untainted youth—a boy on the very precipice of young manhood, worrying about grades, rushing to athletic training with Megumi, and enduring Nobara’s lectures on fashion and music.

 

 He was open, full of trust toward the world, and still carried that boyish light in his eyes.

 

But tonight, in the shadow of the long hallway, sat a third person.

 

Leaning against the edge of an armchair in the darkness of the living room, a man who had been released from a maximum-security prison just a few days ago watched them. 

 

Sukuna. Jin’s twin brother, a man whose very name had been erased from family conversations for years. He possessed the exact same face as Jin, but that was where any resemblance ended. 

 

While Jin was reserved and gentle, Sukuna was built like a beast—massive, broad-shouldered, with sharp facial features and deep, dark hollows beneath his eyes that spoke of years spent under dimmed prison lights. 

 

Old, rough tattoos crept across his skin from his wrists all the way to his neck, and a long scar on the left side of his jaw bore witness to the street fights of his youth.

Sukuna was the product of absolute rejection. 

 

Born an unwanted child, he grew up on the fringes of society where mercy was a weakness and brutality was the only currency. His psychological makeup was entirely devoid of empathy; he divided the world into predators and prey. 

 

He had ended up in prison for severe, reckless violence and running underground operations, where his cold-blooded nature became legendary. No one had ever loved him, nor had he ever sought love. To him, people were either tools or obstacles. He was convinced that nothing in this world could surprise him or shift him from his cold, calculated detachment.

 

And then, fifteen-year-old Yuuji stepped into the room.

 

When the boy caught sight of the stranger who looked so much like his father, his smile faltered for a fraction of a second, but it quickly returned, filled with a timid, warm kindness.

 

"Oh... do we have a guest?" Yuuji asked, looking back and forth between Jin and the massive figure slowly rising from the armchair.

 

"Yuuji... this is your uncle, Sukuna," Jin’s voice was unusually quiet, tense, as if walking on thin ice. "He got out... he came back to town a few days ago. He has some business left here, so he’ll be having dinner with us."

 

Sukuna didn't utter a single word. His dark, sharp, predatory eyes locked onto the boy, dissecting every detail of his appearance with pathological precision. Never in his life had Sukuna felt an attraction toward men; women to him were merely disposable commodities, objects for quick, physical release without a shred of emotion. 

 

But Yuuji... Yuuji triggered something sick, instantaneous, and terrifyingly deep within him.

 

As the boy approached the table, extending his hand ("Nice to meet you, uncle"), Sukuna felt his gut wrench with a wild, possessive hunger.

 

 He observed the anatomy of that fifteen-year-old body with a fixation that bordered on madness. What completely transfixed him was the harsh, cruel contradiction between Yuuji’s obvious physical strength and his absolute, blossoming innocence.

 

 The boy had athletic, well-developed shoulders from daily training and the firm, healthy stride of an athlete, yet the skin on his neck and cheekbones remained soft, flushed, without a single doubt regarding human malice. 

 

That fresh scent of youth, soap, and light sweat from training acted on Sukuna more intensely than any drug he had ever sampled on the streets. Above all, Sukuna was drawn to the boy's total oblivion to his own vulnerability; Yuuji stood before the worst kind of human predator with a smile, completely exposed, offering his pure, unblemished energy on a platter. 

 

Sukuna didn’t just want to look at that light; a sadistic need arose in his psychopathic mind to break that purity, to systematically defile it, and to become the sole, absolute master of that young life.

 

Dinner passed in a heavy, asymmetric silence. Jin attempted to carry a formal conversation, while Yuuji, starving after school, cheerfully babbled about how he and Megumi had barely escaped detention today after being late for class, and how Nobara had forced him to carry her bags after school. 

 

Sukuna sat across from him, tearing the homemade bread with his thick, tattooed fingers. He didn't eat much. He just watched the way Yuuji’s flushed lips moved, how his strong throat swallowed the food, and how his eyes crinkled with genuine, ringing laughter. That image of a child who believed the world was a safe place burned into his skin like a branding iron.

 

When dinner ended, Sukuna stood up and walked out into the cold October night without a word of farewell. 

 

His head was on fire. This sick, incestuous hunger for his own underage nephew left him furious and frenzied.

 

Angry at himself, Sukuna got into his car and drove to the filthiest part of town, straight to the apartment of one of the women who had waited for him while he was behind bars. 

 

He needed sex. A quick, rough, dirty physical act to flush this pink-haired boy out of his head and return him to his usual, cold reality. The woman welcomed him with a subdued smile, accustomed to his harsh nature and ready to cater to his roughness. 

 

The moment the door closed, Sukuna pinned her against the wall without a single word, burying his fingers deep into her hair and pulling her head back with a wild, mechanical rage.

 

But the moment he was supposed to finish what he started, Sukuna froze completely. His body refused to comply. Every time he closed his eyes, it wasn't a woman's body that appeared before him, but the image of Yuuji’s neck under the dim light of Jin’s kitchen.

 

 He saw that flushed, warm skin pulsing with life, reminding him of the scent of the boy's youth. 

 

The perfume, sweat, and cheap makeup in the room suddenly became repulsive to him, organically intolerable and heavy compared to the purity that had captured his senses.

 

 Frustration and fury exploded inside him. With cruel force, Sukuna shoved the woman away so hard that she fell to the floor beside the bed, left in total shock and silence. 

 

Without a single word of explanation, he grabbed his heavy jacket and stormed out of the apartment, slamming the door behind him so violently that the hallway glass rattled.

 

He threw himself back into his car, slammed the door, and remained sitting in the absolute darkness of the cabin. The air in the car was freezing, but Sukuna was suffocating from his own heat. 

 

His hands on the steering wheel trembled—not from the cold, but from the intensity of an arousal and rage he had never felt before, not even in the bloodiest street clashes. 

 

His thoughts were completely contaminated by his nephew. He leaned his head back against the leather seat, closed his eyes, and breathed heavily, shallowly, as every second of the dinner replayed through his mind: Yuuji’s half-open lips as he laughed, the way his sweaty training shirt clung to his developed shoulders, and that soft skin just above the collarbone that he so desperately wanted to bite until it bled.

 

His large  hand slowly drifted downward, unbuckling his belt and sliding over his own body with a heavy, dark longing. He gripped himself roughly through his underwear, and then directly, skin-to-skin, beginning swift, rhythmic, and relentless motions. 

 

Every squeeze of his  fingers was driven solely by that sick image of the boy. As he touched himself in the tight, dark space of the cabin, the rhythm of his body brought back a sharp, cold memory of his prison days.

 

 That same, heavy motion of his hand, those same muffled gasps in the dark—that was how he had spent years in the solitary confinement of maximum security. 

 

There, behind bars, he did it often, mechanically and angrily, using cold fantasies of violence and domination over his enemies merely to expend excess energy and maintain control over his mind in absolute isolation. It had been a release devoid of any depth, the routine of a caged beast passing time between grey walls.



But now, in the darkness of the car, as his hand slid down his own body with that same practiced, heavy rhythm from prison, everything was different.

 

 This was no longer the simple release of a savage inmate; this was a pure, feverish obsession. Each time he tightened his grip around himself, he imagined he was holding Yuuji’s developed shoulders, pinning him against that very same kitchen table and breaking his teenage innocence under the weight of his body. 

 

Sukuna’s breathing grew louder, losing his famous, calculated detachment to the sheer force of the perverse images flooding his mind. 

 

His pride and his body pulsed with brutal excitement, and the thought that the boy had absolutely no idea what was coming for him drove him over the edge. 

 

With a muffled, rough growl that shattered the silence of the car, Sukuna came, his hand left heavy and slick in the dark.

When his breathing finally began to slow and his hand fell limply beside the seat, Sukuna opened his eyes.

 

 His gaze was cold, fixed on the windshield, and a sinister, victorious smile formed on his lips. If Yuuji was the only one who could jumpstart his dead blood, then Yuuji no longer stood a chance. He would be his, at any cost.

 

The next morning, it all began.

Yuuji left the house at seven o'clock, completely unaware of the darkness that had loomed over his life. 

 

He ran toward the station, laughing as he spotted Megumi from afar with his hands in his pockets and Nobara fixing her hair while looking at her phone screen's reflection. 

 

An idyllic teenage life—school, boring classes, loud conversations during breaks, and heavy athletic training in the afternoon where Yuuji gave his all to achieve the best possible result.

 

And across the street, behind the tinted windows of a black car parked in the shadow of the treeline, sat Sukuna.

His gaze tracked the boy’s every step. He watched as Yuuji carelessly threw an arm over Megumi’s shoulders, and felt his fingers grip the steering wheel tight as the thought crossed his mind of how he would have to break those foreign, childish hands if they ever touched what belonged to him. 

 

Sukuna began to keep a detailed log. He knew when Yuuji had classes, where he spent his breaks, which route he took to the stadium, and exactly what time he returned home.

 

The first phase of his twisted game was set. Yuuji was still running after the ball and laughing with his friends, completely unaware that the beast unleashed from its cage had already circled his school, and that the noose around his innocence was slowly, but relentlessly, tightening.