~~Forbidden Brotherly Desire~~ (Pt 1)
what happens when a cuntboy, who hate and disgust his body, eventually feel gifted and the main reason is YOU?
yeah, you heard it right. A CUNTBOY!!!!!
top!male reader, yandere bottom cuntboy, masturbation, stepbrother relationship, milky breasts, own character?, minor character, desperate character, needy character, size difference, sub bottom, jealous bottom, first time writing.
Part 2 / Part 3 / Part 4 / Part 5 / Part 6 / Part 7 / Part 8
Yuta stared at his reflection in the full-length mirror of his bedroom, his small hands clenched into fists at his sides. The body staring back at him was a betrayal—a curse disguised as flesh. His chest heaved with heavy, huge breasts that strained against the loose fabric of his oversized shirt, their milky weight pulling at his shoulders, full and swollen like overripe fruit begging to be plucked. Below, his hips flared out into a big round ass that jiggled with the slightest movement, soft and plush, leading down to thighs that rubbed together with every step. And hidden beneath his panties, that plump juicy cunt, always embarrassingly slick, lips puffy and inviting in a way that made his stomach twist with disgust. Why me? he thought bitterly, tears pricking at his eyes. His parents had done this to him—born with these special genes that twisted him into something neither boy nor girl, but a freakish blend. He hated touching himself, hated even looking, avoiding mirrors like they were poison.
His father had tried to explain it once, mumbling about rare genetics and how Yuta was 'unique,' but words like that only fueled the rage. Yuta spent his days huddled in his room, bratty and withdrawn, snapping at anyone who dared get close. School was a nightmare; whispers followed him, eyes lingered on the way his uniform clung to his curves. He was barely into his teens, small and underdeveloped in ways that made him feel even more monstrous.
Then everything changed. His father remarried—a kind woman, who came with a son of her own. Y/N was everything Yuta wasn't: tall and broad-shouldered, with an easy smile and carefree laugh that filled the house like sunlight. At sixteen, Y/N was already towering over Yuta, his extroverted energy pulling people in effortlessly. From the first day, Y/N sought Yuta out, knocking on his door with a grin. "Hey, little bro! Wanna play some games?" he'd say, ignoring Yuta's sullen glares and sharp retorts.
Yuta resisted at first, crossing his arms over his chest to hide the embarrassing swell of his breasts, his cheeks burning. But Y/N was persistent, dragging him into video games or forcing him to watch movies on the couch. Their parents beamed at the sight—Yuta's brattiness melting away, replaced by shy glances and tentative smiles. As years passed, Yuta's attachment deepened. Y/N was turning into an adult now, his body filling out with muscle, his voice deepening into something that sent shivers down Yuta's spine. Yuta, still clinging to the edges of adolescence, felt his heart race whenever Y/N was near. A brotherly pat on the back made his skin tingle; Y/N's voice calling his name turned him into a stammering mess, face flushing hot as he hid behind his hair.
It started innocent enough. Yuta trailing after Y/N like a shadow, jealous of how his stepbrother lit up rooms with his charm. But lately, the feelings twisted into something darker, more urgent. Yuta knew it was wrong—Y/N was his oni-chan, family now—but the ache in his core wouldn't fade. He'd catch himself staring at Y/N's strong arms, imagining them wrapped around him, or watching the way his stepbrother's shirt clung to his chest after a shower.
One night, barely a teen and alone in the dim glow of his bedside lamp, the pressure became too much. Y/N had left his gym clothes in the laundry basket—a sweaty t-shirt and shorts, reeking of musk and salt. Yuta's hands trembled as he snatched them, heart pounding. He buried his face in the fabric, inhaling deeply, the scent flooding his senses like a drug. Oni-chan~~ The thought of Y/N's body, tall and powerful, made Yuta's breath hitch. For the first time, he didn't recoil from his own touch. His fingers slipped under his nightshirt, brushing the heavy undersides of his milky breasts. They were so full, nipples hardening into peaks as he squeezed, a soft whimper escaping his lips.
Emboldened, he tugged down his panties, exposing his plump juicy cunt. It glistened already, folds slick and swollen, begging for attention he’d always denied. Yuta spread his legs, the big round cheeks of his ass pressing into the mattress, jiggling as he rocked his hips. He rubbed his clit tentatively at first, then harder, imagining Y/N's hands there instead—rough, claiming. The stolen shirt muffled his moans as he sniffed deeper, fingers plunging into his wet heat, stretching himself on the fantasy of his stepbrother's cock. His breasts bounced with each thrust, milk beading at the tips from the intensity. He came hard, body convulsing, cunt clenching around nothing as waves of pleasure crashed over him. Tears mixed with sweat; guilt followed, but so did a spark of something new—desire.
From then on, it became a ritual. Every night, Yuta stole something of Y/N's—a sock, underwear, whatever he could grab—using it to fuel his secret sessions. He'd grind against the fabric, pinching his nipples until they leaked, fucking himself with desperate fingers while whispering Oni-chan, please… Jealousy gnawed at him too. Y/N was so outgoing, always surrounded by friends—guys slapping his back, girls giggling at his jokes. Yuta seethed from the sidelines, clinging tighter, his touches lingering a beat too long.
But the real shift came as Yuta's body began to develop. What he once hated now felt like a gift, a tool to draw Y/N in. His breasts grew even heavier, swaying hypnotically when he walked; his ass rounded out fuller, jiggling with every step; his cunt ached constantly, juicy and ready. This body could make him want me, Yuta thought, tracing his curves in the mirror without flinching. He started training in secret—squats to firm his ass, stretches to accentuate his hips—all for Y/N to notice, to use.
His first seduction attempt was clumsy. Dressed in a tight tank top that barely contained his milky tits, nipples poking through, Yuta 'accidentally' bent over in front of Y/N while reaching for a remote. His shorts rode up, exposing the plump swell of his ass cheeks. "O-Oni-chan, can you help?" he stammered, flushing as he wiggled just a bit.
Y/N chuckled, oblivious, handing him the remote with a ruffle of his hair. "Sure thing, little one. You're getting taller—almost as clumsy as me!" No spark of desire, just brotherly affection. Yuta's heart sank, but he tried again days later, 'tripping' into Y/N's lap during a movie night, his soft breasts pressing against his stepbrother's chest, cunt throbbing against Y/N's thigh through thin fabric.
"Whoa, easy there," Y/N laughed, steadying him with strong arms. "You okay, little bro?" He didn't pull away immediately, but there was no heat in his touch—just concern. Yuta mumbled an excuse and fled, frustration boiling over into another frantic masturbation session, this time with Y/N's pillow clutched between his thighs, humping it until his juices soaked through.
He kept trying, each failure chipping at his confidence. A shared bath where Yuta lingered naked, water lapping at his heavy breasts and the inviting slit of his cunt, hoping Y/N would stare. Instead, Y/N scrubbed his back like it was nothing. Walking around in just underwear, ass cheeks bouncing, breasts spilling over the cups— Y/N complimented his 'growth spurt' with a grin, clueless.
Yuta's fantasies grew hopeless, vivid. He'd picture Y/N finally snapping, pinning him down, sucking on his leaking nipples while pounding into his juicy cunt, that big round ass slapping against Y/N's hips. "Use me, Oni-chan. Fuck your little brother's slutty holes!" But reality was cruel; Y/N doted on him like a kid brother, letting Yuta cling and cuddle without suspicion, even when Yuta's hands wandered a little too low.
One evening, as Y/N prepared for his birthday party—turning adult, surrounded by friends—Yuta watched from the doorway, jealousy twisting like a knife. Y/N's laugh boomed, his tall frame drawing everyone in. Yuta's body hummed with need, breasts aching, cunt dripping into his panties. He slipped away to Y/N's room, snatching a fresh shirt from the drawer, already plotting tonight's release. But deep down, he wondered—how much longer could he hide this burning, taboo hunger before it consumed them both?
Part 2 / Part 3 / Part 4 / Part 5 / Part 6 / Part 7 / Part 8