Izuku lingered after the final bell, his fingers white-knuckled around the strap of his backpack. The classroom emptied around him until it was just the sound of his own breathing and the slow, deliberate scrape of chalk as Mr. Bakugo cleaned the board. He didn’t turn around. “You’re blocking the door, problem child.”

“I have a question,” Izuku blurted, the words too loud in the quiet. He winced at his own volume.

Katsuki finished the last line, dusted his hands on his trousers, and finally turned. He leaned back against the teacher’s desk, crossing his arms. The late afternoon sun cut across his sharp features, catching the red of his eyes. He didn’t smile. “Obviously. Spit it out.”

“It’s about… the lesson. From before.” Izuku’s gaze dropped to the floorboards, to the stripe of gold light between them. “You taught me about… mine. But I don’t… I’ve never seen…” He swallowed, his throat clicking. “A boy’s. I don’t know what one looks like. Not really.”

Katsuki was silent for a long moment, a predator perfectly still. Then he pushed off the desk. “Curiosity is the foundation of learning.” He walked to the classroom door, turned the lock with a definitive click. The sound echoed. He didn’t return to the desk. He stood in the open space near the windows, the dust motes swirling around him like a halo. “Come here.”

Izuku obeyed, his legs carrying him on autopilot until he stood a few feet away, close enough to smell the clean, sharp scent of his teacher’s soap. Katsuki’s hands went to his belt. The leather slid free with a whisper. The button of his trousers popped. The zipper rasp was the only sound in the world.

“Pay attention,” Katsuki said, his voice a low growl. He pushed his trousers and briefs down just past his hips. He was soft, resting against his thigh. It was… substantial. Thick. A heavy, flushed weight. Izuku’s breath hitched. The skin was smooth, a deep pink, and at the tip—a fold of skin, a hood, covering the head. Below, his balls were full, a heavy sac nestled in coarse blond hair.

“This,” Katsuki said, his hand not touching, just gesturing, “is what you asked to see. The basic anatomy.” His eyes were locked on Izuku’s face, watching every flicker of thought. “Most are cut. The foreskin is removed. Mine isn’t.” As he spoke, a change began. A twitch. A slow, inevitable thickening. The soft flesh began to swell, to rise, the skin stretching taut. Izuku watched, mesmerized, as it grew, lifting away from his thigh, curving upward. The hood began to retract on its own, peeling back to reveal a slick, plum-dark head, beading with a single pearl of moisture at the slit.

It was massive. Fully hard, it stood thick and angry against Katsuki’s lower stomach, a veined, rigid column of flesh. Izuku’s mouth went dry. He’d seen diagrams. They were lies. “It’s… big,” he whispered, the understatement of his life.

“It is.” Katsuki’s own breath was deeper now. He finally wrapped his hand around himself, his fingers not meeting. He gave a slow, practiced stroke, from root to tip, his thumb smearing the bead of pre-cum. “This is the shaft. The head. The frenulum, here, underneath—sensitive.” He turned his hand, showing Izuku the swollen veins, the tight pull of skin. “And these,” he said, cupping his balls with his other hand, weighing them, “are what hold the seed. They get full. Ache. Especially when I look at something I want to ruin.”

Izuku couldn’t look away. His own body was responding, a familiar heat pooling low in his belly, a dampness he could feel seeping into his boxers. “Kacchan,” he breathed, the secret name slipping out in his awe.

A muscle jumped in Katsuki’s jaw. His strokes slowed, became possessive, a display of control and function. “That’s the word, isn’t it? The one that makes you drip. Say it again.”

“Kacchan,” Izuku repeated, louder, his eyes glued to the mesmerizing slide of his teacher’s fist. “Does it… feel good? When you touch it?”

"It feels like pressure," Katsuki said, his voice a rough scrape in the quiet room. His fist moved in a slow, relentless rhythm, the skin of his cock glistening. "A building ache right here." He thumbed the swollen head, smearing more wetness. "The need to release. To push into something hot and tight. You're staring. Are you wet for it, problem child?"

Izuku's nod was a jerky, helpless motion. "Y-yes, Kacchan."

"Prove it." Katsuki's hand stilled, gripping himself at the base. "Pants. Off. Now."

Izuku's fingers fumbled with his uniform trousers, the button popping free. He shoved them down his thighs along with his boxers, the air cool on his damp skin. He stood there, exposed from the waist down, his thick thighs trembling. His pussy was a neat, bare slit, already glistening, his clit a prominent, eager bud.

"Good," Katsuki growled, his face eyes dark as they raked over the boy. "Now touch yourself. Mirror me. Learn the rhythm." He resumed his strokes, long and firm, a visual lesson. "Watch my hand. Then watch yours."

Izuku's hand shook as he brought it between his legs. His fingertips brushed his own wetness, a shocked gasp leaving his lips. He mimicked the motion, a clumsy slide over his slick folds, circling his clit.

"Eyes on me," Katsuki commanded, his own gaze locked on Izuku's face. "Don't look down. Look at what you're doing this for." His pace increased slightly, the wet sound of his fist on his cock punctuating the silence. "This is mutual. You get off on my cock. I get off on your cunt. We're connected. Even like this."

Izuku moaned, his head falling back for a second before he forced his eyes back to his teacher's. The visual was overwhelming—Katsuki, fully dressed from the waist up, shirt crisp and tucked, his massive cock jutting from his open trousers, his hand working it with brutal efficiency. And Izuku, half-undressed, legs spread, fingers sliding in his own wetness, completely on display.

"Kacchan," Izuku whimpered, his hips beginning to stutter forward into his own touch. "It's… it's different. When I watch you."

"It's supposed to be," Katsuki said, a bead of sweat tracing his temple. "Your body knows its purpose now. It knows this cock. It's preparing for it." He spread his legs wider, a blatant, powerful stance. "Show me how you prepare. Get those fingers inside. Get them messy."

Izuku obeyed, pushing two fingers into his own tight heat, a choked cry escaping him. He was so wet it was a smooth, slick glide. He pumped them, his other hand braced on his thigh, his eyes wide and glued to Katsuki's furious strokes.

"That's it," Katsuki praised, his breath coming harder. "Make yourself ready for me. Imagine it's my cock stretching you open. You think you can take it? This?" He gave himself a particularly rough pull, his length throbbing in his grip. "You'll have to. I'll make you."

The room filled with the sounds of them: Izuku's wet, squelching rhythm, Katsuki's faster, rougher friction, their mingling breaths. Izuku's free hand flew to his mouth, biting his knuckle to stifle a louder moan.

"None of that," Katsuki snapped. "I want to hear you. I want to hear what I do to you. Let go."

Izuku's hand dropped, a desperate, broken sound pouring out of him as his fingers worked faster, curling inside himself. "Kacchan, I'm—I'm close, I can't—"

"You can. You will. Look at me. Come when I tell you to." Katsuki's movements became punishing, his balls drawn up tight, his own release clearly imminent. His crimson eyes burned into Izuku's. "Now."

The command was a detonation. Izuku’s back arched, a silent scream tearing from his throat as his fingers jammed deep and his body shattered. A gush of clear fluid erupted from him, not a trickle but a fountain, shooting out in a startling arc to splatter across the floorboards between his spread feet. It was a violent, soaking release, his thighs trembling as he emptied himself in pulsing waves, his vision whiting out around the edges.

Katsuki’s own climax followed a second later, a guttural snarl ripped from his chest. He aimed, his fist a blur at the base of his cock. Thick, white ropes of cum streaked across the distance, painting Izuku’s glistening, spread-open cunt and his heaving lower belly. The heat of it was a brand on Izuku’s sensitive skin, a shocking contrast to the cool air.

For a long moment, there was only the sound of their ragged breathing. Izuku slumped, his fingers slipping from inside himself, his legs barely holding him. He looked down, dazed, at the mess of them. His own release, clear and slick, pooled on the floor. Katsuki’s, opaque and pearlescent, was smeared across his skin, some strands already dripping down his inner thigh. “It’s… different,” Izuku mumbled, his voice hoarse.

Katsuki was already tucking his spent cock back into his trousers, his movements efficient, though his breath was still heavy. “Of course it is. Yours is just lubrication. A preparation. Mine is seed.” He zipped his fly, his eyes never leaving the canvas of Izuku’s body. “Look at it. Study it.”

Izuku’s hand, still wet with his own slick, hovered over his belly. He touched a cooling strand of Katsuki’s cum, gathering it on his fingertips. It was thicker than he expected, sticky. He brought his fingers to his nose, inhaling the musky, alien scent. His eyes, wide with exhausted curiosity, flicked up to Katsuki’s face. “It smells like you.”

“It is me,” Katsuki said, his voice dropping into that low, instructional growl. “Now rub it in. All of it. Mark your skin with it. Let your cunt taste it.”

Izuku’s breath hitched. He obeyed, spreading the sticky warmth over his lower belly, his hips, then carefully down, smearing it across his swollen folds. The sensation was intimate and degrading and profoundly arousing all at once. His clit, still throbbing, twitched under the touch. He worked it in, mixing Katsuki’s release with his own lingering wetness until his pussy glistened with both.

“Good boy,” Katsuki murmured, the praise landing like a physical touch. He took a step closer, looking down at his handiwork. “Your body accepts it. It’s learning. Remember this feeling. The heat of it. The smell. This is what happens when you obey.”

Izuku’s fingers stilled, buried in the mess. He felt owned. He felt seen. “Kacchan… will it… will it ever go inside?”

Katsuki’s lips curled, not quite a smile. A promise. “When you’re ready. When I’ve trained that greedy little hole to take every inch. It will.” He reached out, not touching Izuku’s skin, but gripping his chin, forcing his gaze up. “This was your second lesson. Your body proved it can come on command. It proved it can be marked. The next lesson,” he said, his thumb brushing Izuku’s bottom lip, “will be about your mouth.”

He released him, turning to retrieve his blazer from the desk. “Clean yourself up. The janitor’s closet has rags and spray. Leave this room spotless. Then go home.”

Izuku stood on shaky legs, the combined fluids cooling on his skin, a tangible reminder. “Yes, Kacchan.”

Katsuki paused at the door, unlocking it. He didn’t look back. “You did well today.” Then he was gone, the door clicking shut behind him, leaving Izuku alone in the silent, sun-striped room, covered in the evidence of his lesson.