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The Professor's Potion

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A crack AU. Two male best friends in college, Hyukjae and nerdy Donghae. Hyukjae was involved in an experiment (by professor Kim Heechul) where he turns into a voluptuous lady after taking the professor concoction. He could turn to male only after someone comes in him. So he could only ask his best friend Donghae to turn him back into a male. Donghae who had always love Hyukjae (even as a male) agreed willingly.

Chapter 3: Virgin Sacrifice

The word “start” hung in the air, a stark, terrifying command. Hyukjae’s gaze was fixed on a point on the opposite wall, his body rigid, awaiting instruction.

Donghae remained rooted to the floor, five feet of scuffed linoleum that felt like a canyon. His heart hammered against his sternum, a frantic drum of fear and something darker, more shameful.This was madness. It was a violation of every silent promise he’d ever made to himself, to Hyukjae, to the friendship that was the bedrock of his life. And yet, he’d volunteered. The momentum of that decision pushed him forward, one reluctant step, then another, until he stood by the bed.

The air between them was charged, thick with the scent of vanilla from Hyukjae’s skin and the musty smell of old paper from Donghae’s sheets. He could see the rapid flutter of pulse in Hyukjae’s throat.

“What’s step one?” Hyukjae asked, the false calm in his voice cracking at the edges. “Protocol.”

“I…” Donghae’s mind was a blank white static. “Clothes. I guess.”

“Right. Okay.” Hyukjae’s hands went to the hem of the oversized grey t-shirt. He pulled it up and over his head in a single, decisive motion, tossing it to the floor. He sat there in just the black sports bra and the jeans. His skin was pale in the dim light, a landscape of unfamiliar shadows and slopes. He didn’t look at Donghae. “Your turn.”

Donghae fumbled with the buttons of his own shirt, his fingers clumsy and numb. The fabric felt like sandpaper. He peeled it off, letting it drop. The cool air of the apartment hit his chest, raising goosebumps. He was shaking.

Hyukjae finally glanced at him, a quick flicker of his eyes. “You’re scrawnier than I remember.”

It was an old joke, a familiar barb. It should have broken the tension. Instead, it sounded brittle, a script they were forcing.

“You’re not,” Donghae retorted, his voice flat. His eyes were inevitably drawn down. The bra was a severe line of elastic and fabric, compressing a shape that defied logic.

Hyukjae followed his gaze and made a frustrated sound. “This fucking thing. I can’t breathe.” His hands went behind his back, fingers struggling with the clasp. He wrestled with it for a moment, a flicker of his old impatience surfacing. “It’s stuck. Help me.”

Donghae moved then, driven by habit. He sat on the edge of the bed, his knee brushing Hyukjae’s thigh. He could feel the heat radiating through the denim. He reached behind Hyukjae, his fingertips finding the small metal hook and eye. The skin of Hyukjae’s back was smooth, warm. He fumbled, his knuckles brushing the knobs of Hyukjae’s spine.

“Hurry up,” Hyukjae muttered, a tremble in his voice.

The clasp gave way with a soft snick. Hyukjae let out a small, sharp breath as the tension released. He shrugged the straps off his shoulders, letting the garment fall forward into his lap. He didn’t remove it, just sat there holding it, staring at the wall.

Donghae stared too. The sight was so profoundly wrong it was almost beautiful. Hyukjae’s chest was bare, the lines soft and full, tipped with pale pink. His skin looked unbearably delicate. Donghae’s mouth went dry. This wasn’t arousal; it was a kind of stunned, clinical horror mixed with a deep, gut-wrenching ache. He’d seen pictures, of course. He’d imagined. This was different. This was Hyukjae.

“The jeans are next, I suppose,” Hyukjae said, his voice tight. He stood up abruptly, the bra dropping from his lap. He unbuttoned his jeans, pushed them and the underwear beneath down his hips in one rough motion, and stepped out of them. He stood naked by the side of the bed, not hiding, not posing. Just standing there, a living violation of nature. “Your turn. We’re doing the protocol. All the way.”

Donghae’s jeans felt like a prison. His body was responding now, a treacherous, low thrum of heat in his belly, a tightness in his groin that filled him with self-loathing. He stood, turned his back to Hyukjae out of some last shred of modesty, and stripped off the rest of his clothes. The air was cold on his bare skin. He was half-hard, a fact that felt like the deepest betrayal.

He turned back. Hyukjae was looking at him now, his gaze dropping for an instant before snapping back up to his face. A faint, sickly smirk touched his lips.“See? Mechanics. All systems seem operational.”

“Hyukjae, stop.” The plea was torn from him.

“Why? It’s a joke. It’s all a fucking joke. Let’s laugh.” But there was no laughter in his eyes. Only a flat, desperate terror.

Donghae moved towards the bed. Hyukjae climbed onto it, lying stiffly on his back in the center, staring at the ceiling. The posture was so unnaturally rigid it looked like he was lying in state.

“This isn’t right,” Donghae whispered, standing beside the bed.

“It’s the only thing that’s right,” Hyukjae countered, his jaw clenched. “Get on with it.”

Donghae lowered himself onto the bed, his weight causing the mattress to dip, rolling Hyukjae slightly toward him. The scent of him was overwhelming this close. He braced one hand on the pillow beside Hyukjae’s head, his body hovering. Their faces were inches apart. Hyukjae’s breath was fast and shallow, puffing against Donghae’s lips.

“Look at me,” Donghae said.

Hyukjae’s eyes, wide and dark, shifted to meet his. In them, Donghae saw the same boy who’d climbed a campus fence with him last spring, who’d cried during a stupid sad movie and tried to hide it. He saw his best friend. The sight gave him a surge of terrible, decisive courage.

He lowered his head and kissed him.

It wasn’t a romantic kiss. It was a collision. Hyukjae’s lips were soft, parted in surprise. He made a small, muffled sound against Donghae’s mouth. For a second, he was utterly still. Then his hands came up, not to push away, but to clutch at Donghae’s shoulders, fingers digging into the muscle there.The kiss changed. The pretense of procedure shattered. It became hungry, messy. Hyukjae opened his mouth and Donghae surged in, tasting coffee and the metallic tang of fear. Hyukjae’s tongue met his, a hesitant slide that quickly turned frantic. The rigid line of Hyukjae’s body softened, melting into the mattress, arching up into Donghae’s weight.

Donghae broke the kiss, gasping for air. He trailed his mouth down Hyukjae’s jaw, to his throat, feeling the frantic pulse there under his lips. He kissed the hollow at the base of his throat, then lower. His hand, of its own volition, came up and covered Hyukjae’s breast. The flesh was heavy, soft. Hyukjae jerked beneath him, a full-body flinch, followed by a low groan.

“Fuck,” Hyukjae breathed out, the word shuddering.

Donghae circled the peak with his thumb, feeling it tighten into a hard point. He bent his head and took it into his mouth.

The sound Hyukjae made was raw, torn from somewhere deep. His back arched off the bed, his hands flying to tangle in Donghae’s hair, not pushing him away but holding him there. “Oh, god. Oh, fuck. That’s… I can feel that everywhere.”

Donghae swirled his tongue, the taste of skin and salt filling his senses. He was fully hard now, his erection pressing against Hyukjae’s thigh. The “protocol” was a distant memory, incinerated by the heat in his veins.

His other hand slid down the trembling plane of Hyukjae’s stomach, over the curve of his hip. The skin was fever-hot. He traced the line where thigh met torso, his fingertips brushing coarse, unfamiliar hair.

Hyukjae’s legs fell open, a silent, yielding invitation. His breath was coming in ragged pants. “Don’t stop. Just… do it.”

Donghae’s fingers probed lower, through the soft hair, finding slick, startling heat. Hyukjae gasped, hips bucking.

“You’re wet,” Donghae murmured against his skin, the observation shocking him.

“It’s the body,” Hyukjae panted, his voice thick with shame and need. “It’s not me. It just… happens. Do it, Donghae. Please.”

The ‘please’ broke him. He shifted his weight, kneeling between Hyukjae’s spread thighs. He looked down. The sight of Hyukjae laid bare for him, glistening and open, was the most obscene, beautiful thing he’d ever seen. He took himself in hand, his fingers slippery from Hyukjae’s wetness. The head of his cock nudged against the entrance.

“Tell me if I hurt you,” he whispered, his voice ragged.

He pressed forward.

The resistance was tight, yielding. Hyukjae’s body clenched around him, a hot, impossible vise. Hyukjae cried out, a sharp, pained sound, his nails scoring Donghae’s back.

“Wait, wait, fuck, wait—” Hyukjae choked out.

Donghae froze, buried to the hilt, trembling with the effort of holding still. The sensation was overwhelming—tight, scorching heat, a fullness that made his vision blur. He looked down at Hyukjae’s face, which was contorted, tears leaking from the corners of his eyes.

“Breathe,” Donghae gritted out. “Just breathe.”

Hyukjae nodded, gulping air. The fierce tension in his body began to ease, incrementally. The painful grip around Donghae softened into a pulsating, rhythmic clutch.

“Okay,” Hyukjae whispered, his eyes still squeezed shut.“Okay. Move.”

Donghae drew back, a slow, dragging slide that made them both groan, then pushed forward again. The second stroke was easier, wetter. Hyukjae’s breath hitched, and this time the sound wasn’t just pain. It was surprised pleasure.

He set a rhythm, shallow at first, then deeper. The bedsprings began a low, rhythmic protest. The air filled with the sounds of skin slapping against skin, ragged breathing, muffled gasps. Donghae dropped his head to Hyukjae’s shoulder, biting back his own moans against the warm skin.

Hyukjae’s legs came up, wrapping around Donghae’s waist, heels digging into the small of his back, pulling him deeper. “Harder,” he demanded, his voice a guttural rasp that held none of its former pitch. “Stop being so fucking careful.”

Donghae obeyed. He drove into him, each thrust a jolt that shook the bed frame. He was losing control, the careful construct of his mind dissolving into pure sensation. The coil in his gut wound tighter, a throbbing, urgent pressure.

Hyukjae’s hands scrambled over his back, down to his ass, gripping, urging him on. “Yes, like that, right there, fuck—!”

The crude, desperate words ignited something primal in Donghae. He fucked him in earnest now, a relentless, pounding pace. Hyukjae was meeting him thrust for thrust, his head thrown back, a string of obscenities and pleas falling from his lips in a continuous stream. It was filthy. It was real.

Donghae felt Hyukjae’s inner muscles begin to flutter, a frantic, rhythmic clenching. Hyukjae’s whole body went rigid, a silent scream etched on his face as he came, his cunt milking Donghae in fierce, contracting waves.

The sensation tipped Donghae over the edge. With a choked, ragged cry that was half-sob, half-roar, he buried himself deep and let go. His orgasm tore through him, white-hot and devastating, pumping into Hyukjae’s body in pulsing spurts. He collapsed onto him, his weight pinning Hyukjae to the mattress, his face buried in the sweat-damp pillow beside Hyukjae’s head.

For a long time, there was only the sound of their heaving breaths and the ringing in Donghae’s ears. The world slowly solidified around them—the rumpled sheets, the slant of morning light now strong through the blinds, the stickiness between their bodies.

He was still inside him. Slowly, gently, he pulled out. The wet sound was obscenely loud.

Hyukjae lay motionless beneath him, eyes closed. Tears had tracked clean lines through the sweat on his temples. Donghae rolled off, onto his back, staring at the water-stained ceiling. The cold air chilled the sweat on his skin. He felt hollowed out, scraped clean. He felt like a monster.

The protocol was complete. The biological agent had been delivered.

Beside him, Hyukjae stirred. He drew his knees up to his chest, curling onto his side, turning his back to Donghae. His shoulders were shaking silently.

Donghae reached out a hand, his fingers hovering an inch from Hyukjae’s trembling spine. He didn’t dare touch him.

“Hyukjae?” His voice was a wreck.

“Don’t,” was the muffled, wet reply. “Just… don’t talk. Rule number one. We never talk about it.”

They lay there in the ruined bed, in the stark morning light, the silence between them now a vast, frozen desert. The only thing moving was the slow, silent drip of Donghae’s release, tracing a path down the inside of Hyukjae’s thigh. They waited. For the world to right itself. For the change to begin.Nothing happened. The room remained still. The air remained stale. Hyukjae’s body, curled away from him, remained precisely, devastatingly, the same.

The stillness was an accusation. Donghae watched the rise and fall of Hyukjae’s back, waiting for a shudder, a glow, some sign the impossible science was working. Only a faint tremor from held-back tears moved him. The drip on Hyukjae’s thigh was already cooling, a sticky testament to their failure.

An hour passed, measured in the slow crawl of light across the floor. The apartment’s normal sounds—the fridge’s hum, a distant car alarm—intruded, making what they’d done feel small and squalid.

“We need to call again.” Hyukjae’s voice was flat, scraped raw. He still didn’t turn.

“His number’s dead.” Donghae’s own throat felt torn.

“Then we go back. We tear that fucking lab apart.”

“He’ll be gone. You know he is.”

Hyukjae finally moved, uncurling with a stiff, pained motion. He sat up, keeping the sheet pooled in his lap. His face was pale, eyes swollen. He looked at the wall, at the floor, at the discarded clothes—anywhere but at Donghae. “So what? We just wait? See if I start my fucking period? See if this is stable?”

The crudeness was a weapon. Donghae flinched. He sat up too, the sheet falling away. The smell of sex and sweat was oppressive. “I don’t know.”

“Great. Fantastic.” Hyukjae stood, movements sharp with a rage that couldn’t find its target. He strode naked to the small adjoining bathroom, a pale, furious ghost in the morning light. “Don’t follow me.”

The door shut, not a slam, but a solid, final click. The shower started a moment later, a sudden, relentless roar.

Donghae sat in the wrecked bed, the silence now filled with hammering water. He looked at his hands. He could still feel the weight of Hyukjae’s breast in his palm, the clench of his body. The memory was visceral, a series of flashes that burned: the choked cry, the wet heat, the desperate arch of his spine. He’d fucked his best friend. He’d come inside him. And it had meant nothing. It had changed nothing.

He dressed slowly, each article of clothing feeling like a costume. He picked up Hyukjae’s discarded things, folding the stupid grey shirt with mechanical care. The shower ran and ran.

Eventually, the water shut off. Silence returned, thicker now. Donghae stood by the bed, waiting. He didn’t know for what.

The bathroom door opened. Steam billowed out. Hyukjae emerged, a towel wrapped tightly around his chest, his hair dripping dark strands onto his shoulders. He looked cleaner, but somehow more hollow. His eyes were red-rimmed from more than water.

He stopped a few feet from Donghae, staring at a point on his chest.

“Well?” Hyukjae’s voice was a quiet ruin.

Donghae had no answer. He took a step forward, his movement hesitant. He lifted a hand, his fingers trembling slightly, and brushed a damp lock of hair from Hyukjae’s forehead. The skin was hot from the shower. He leaned in and pressed his lips there, a dry, chaste touch that felt like a funeral rite.

“At least we tried,” Donghae whispered, the words ash in his mouth.

Hyukjae’s eyes squeezed shut. A single, clear tear tracked down his cheek, cutting through the steam-flush. He gave a tiny, almost imperceptible nod. Then he turned and walked back into the bathroom, closing the door softly behind him, leaving Donghae alone with the echo of his own hopeless words.

Donghae sank onto the edge of the bed, head in his hands. The roar of water didn’t start again. Only a profound, aching quiet came from behind the door. He listened to the drip of the tap, to the faint sound of rustling fabric. He braced himself for Hyukjae to come back out, wrapped in silence and a towel, for the long, terrible day of pretending to begin.

The door flew open.

It crashed against the wall. Hyukjae stood in the doorway, not wrapped in a towel, but clutching it in one fist in front of him, his body fully exposed. His hair was wild, his eyes wide, blazing with a shock so total it bordered on madness.

“It works!”

The shout was a raw, explosive thing. But the voice—the voice was wrong. It was lower.Rougher. It cracked on the second word.

Donghae stared. His mind refused to process. The shape in the doorway was shifting, not in a glow or a shimmer, but in solid, bewildering reality. The curves were simplifying, melting inwards, the delicate lines hardening into familiar, angular planes. The softness over the chest was pulling back, tight against the sternum, the skin rippling as it reshaped into the taut muscle Donghae knew.

Hyukjae dropped the towel.

He stood there, naked and utterly, completely male. Himself. The broad shoulders, the flat chest with its small, familiar nipples, the narrow hips, the cock lying soft against his thigh—it was all Hyukjae. It was him.

Donghae’s legs gave out. He sat down hard on the bed, his mouth agape.

Hyukjae looked down at his own body, his hands flying to his chest, patting the firm, flat planes. He grabbed his own dick, a rough, disbelieving handful, and a wild, unhinged laugh burst from him—a deep, barking, masculine sound that filled the tiny apartment.

“Holy shit. Holy fucking shit!” He turned, looking at his reflection in the dark television screen, a distorted, shadowy echo of his own form. “Look! Donghae, look!”

Donghae was already looking. He was memorizing. The last traces of the other body were vanishing, the skin settling into its old geography. Only the hair, still damp and long, remained as a ghost of what had been.

Hyukjae spun back to face him, his grin manic, tears of a different kind now streaking his face. “It worked! Your stupid, gross, fucking protocol actually worked!”

He stumbled forward, legs seemingly unsteady on this reclaimed version of himself, and grabbed Donghae by the shoulders, shaking him. “I’m back. Do you see it? I’m me.”

Donghae looked up into that face—the sharp jaw, the familiar mischievous glint in the eyes, the smile he’d loved for years. The body was correct. The relief that flooded him was tidal, washing away the horror, the shame, the guilt. It left behind a profound, dizzying emptiness.

He was looking at Lee Hyukjae. His best friend. The person he’d just had raw, sobbing sex with. The person he’d loved in secret for what felt like forever.

And they had just agreed to never speak of it again.

“Yeah,” Donghae said, his own voice strangely calm. He forced a smile onto his numb face. “I see. You’re you.”

Hyukjae’s triumphant laughter filled the room, bouncing off the walls of books, and Donghae knew, with a cold, sinking certainty, that nothing would ever be the same.

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