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The first time it happens is a genuine accident.
It's late afternoon and Katsuki is home alone for the weekend. An unusual occurrence these days. Ever since he and Deku finally moved in together, he's become used to quiet evenings in, spending it bickering and joking, cuddling while watching trashy reality TV that the nerd is obsessed with.
But something had come up and Izuku had gone back home to visit his mother, so it's just him in their modest apartment for the next two days.
Which leads him to his current predicament.
Katsuki's just minding his business when he first sees the incriminating item.
It lies on the floor of their shared bathroom, stark against the white tiles and impossible to miss. A pair of panties.
It's not risqué or scandalous or anything skimpy. Rather, it's practical and functional, a plain pink in colour with a tiny bow on the front. Feminine and pretty. And completely out of place.
It has Katsuki stopping dead in his tracks.
His eyebrows raise, a myriad of thoughts whirling in his head as his heart rate picks up at the sight.
It's not his, clearly. And neither he nor Izuku has had anyone over recently for them to be leaving underwear on the floor of their bathroom. So by process of elimination, it's Izuku's then. He's the only person other than Katsuki himself who uses their cramped little bathroom.
Katsuki licks his lips, eyes still focused on the pink scrap of fabric lying innocently at his feet. He shouldn't be thinking this. Obviously, this is a fucking accident. Something the nerd doesn't want people to know and has kept secret all these years– Katsuki would know otherwise. The two of them have been attached at the hip since they were shitty toddlers after all. They've shared bathrooms and locker rooms, changed together, lived together; if Izuku was comfortable with people knowing, Katsuki would know.
Which is exactly why he should just move the suspicious article of clothing to the laundry hamper and forget about it. Act like he never saw it, like he doesn't know it exists.
Except– he can't stop looking at it.
Unbidden, images flash through his mind of Izuku wearing it. The more he stares at it, the more vivid and high clarity those images become, and consequently, the more his dick starts to rise in interest.
He pictures the soft fabric being stretched over thick thighs and pulled up until they sit snug against Izuku's crotch; wrapped around rounded hips, hugging that fat, freckled ass and cupping his pussy.
He'd look so good. So pretty and feminine. Katsuki's babygirl. He wonders if the nerd would like to be called that.
Katsuki bends down to pick it up. Slowly, cautiously. It's thin and soft. He pauses, silently warring with himself. He shouldn't. But his self restraint crumbles like a castle made of sand and he gives in to the temptation to bring it up to his nose. His dick, which was already half-hard, chubs to full mast in record time, bulging out uncomfortably in his sweatpants.
He takes a long whiff of it, pushing his nose firmly into the crotch of the panties and groaning loudly when Izuku's scent floods his nose. It's strong. Sweet, musky and smelling like pure sex.
Katsuki can't resist. He presses the panties into his face, holding it there and breathing in deep like an adict unable to control himself.
"Fuuuck..."
Surely, no one would fucking know if he just–
Fuck it. He shoves his free hand into his boxers, taking his dick in hand and starting with a solid squeeze to his aching shaft. He's wet with pre-cum and hot, hot, hot, his cock throbbing in his grip.
His back hits the bathroom door and he slides down to the floor, spreading his legs and closing his eyes as he slowly jerks himself. He works his cock out of his sweats, pumping to a steady rhythm while progressively more sinful visions dance behind his eyelids.
The Izuku in his fantasy is nude now. Sly and seductive, sitting on Katsuki's bed wearing nothing but his tiny pink panties and a saucy smile. He looks so fucking cute and sexy, Katsuki wants to eat him.
He wants to grab those gorgeous legs, yank them open and press his face to Izuku's covered pussy. He'd be wet down there, Katsuki bets. Would definitely be the type to absolutely soak his underwear, to have slick drip out of his hole and run down his thighs. Would he be a squirter? Katsuki could absolutely make him squirt.
He pumps his cock faster, his grip turning hard, then slowing down. He traces a thumb down the prominent vein that runs under his shaft and moans, head audibly thumping against the closed door at the sudden burst of pleasure that shoots through him.
He takes another huff of the fabric scrunched in his fist. He's smelling Izuku's pussy, fuck.
Katsuki wonders what the nerd would look like sprawled out under him.
What would his cunt look like if he pulled those panties to the side? He'd place good money on them being plump and juicy. Deku is thicc as fuck so it's not unreasonable to imagine a chubby pussy, right? Hairless and flushed, with fat pussy lips that glisten with sticky slick. He'd probably have the pinkest little hole hidden in between when Katsuki spreads them open and takes a look.
He can see it so clearly, how shy Deku would get letting Katsuki open him up like that. Face red as a tomato, his arms flailing wildly while Katsuki lays between his legs and parts his tight little pussy to lick inside him. To suck and slurp and devour that slutty little cunny until it's drooling, gaping, quivering– Izuku screaming in pleasure under the assault of his fingers and tongue. Screaming to stop, screaming for more. Screaming because it's good.
"Oh fuck. Izuku–"
Just thinking about it has him ready to bust. He has to break rhythm and circle the base of his dick to stop himself from cumming then and there like some inexperienced teenager seeing pussy for the first time.
When he calms enough to open his eyes and look down at his lap, he has to bite back another groan. His dick is an angry red now, the swollen mushroom head shiny with pre cum beading at the tip.
He wraps the panty around his dick, tentatively moving it over his arousal. He's big. Katsuki knows he's big, he's been told so by the random extras he sometimes fucks when he's really pent up. But he's so turned on right now, he doubts he'll even fit inside Izuku's throat or his pussy and definitely not in his ass. Not without considerable prep.
But it would be so fucking heavenly. To fuck him. Actually, properly fuck Izuku. He'd be virgin tight, like a vice grip, his silky inner walls milking his cock like no tomorrow. Hot and wet and just perfect.
He rubs his slit. More pre cum dribbles out, trailing down his long shaft and seeping into the slowly dampening fabric of Izuku's panties. Katsuki increases the pace. He brings his free hand to cup his balls. They're swollen and round, resting heavy on his thighs. It feels good to play with them.
Maybe Katsuki could get Deku to play with his balls a bit? Mouth at them, licking and suckling, before he sucks Katsuki's dick.
A new thought emerges.
How exactly would Izuku be in bed?
Katsuki can see it both ways.
As a little minx, all coy and unassuming. He'd be a freak though– would suck Katsuki's soul out his dick then ride his face, shameless and wanton as he smushes his pretty pussy all over his Kacchan's face. He'd be down to try anything– different positions, different kinks, in different holes. Might even tie Katsuki down and fuck himself on his dick, use him as a dildo. Maybe Katsuki could buy him more revealing lingerie, and call him pretty and beautiful. He'd like that. He'd be Kacchan's precious little slut.
Or. Or would Deku be a pillow princess? Would he get too cockdrunk to participate? That sharp, analytical mind that's always on, always running– maybe he'd get so overwhelmed and overstimulated that he can't do anything but lie there and just take it. Dumb and drooling, happy to let Katsuki take care of him. He'd be a pretty crier, begging his Kacchan for more, to fuck him full and deep. To make him cum because he's so empty. A needy, desperate thing that's hungry for cock.
Katsuki's close now. He's pistoning his fist over his cock in tandem with massaging his balls. He's on that steep edge, standing at the precipice ready to tumble over. To cum– he needs to cum. The slide of Izuku's panties feels so fucking good. He'll cum on it. His balls twitch at the thought, his hands practically flying over his stiff shaft.
One final image invades his mind, burning itself onto the back of his eyes. Izuku laying fucked out on his bed, his tongue lolling out and eyes rolled back, pink panties pulled aside to reveal his uncontrollably fluttering pussy– creampied. Leaking rivulets of thick white cum and slick. Katsuki's cum–
Katsuki comes so hard he see white for a moment. A searing hot wave of pleasure takes him under, rushing through him with such intensity that it leaves him blind and light headed.
He's heavy and boneless when he comes to. Cock flagging and chest heaving, he lays there. The panties are wet with his cum, still clutched tight in his closed fist.
"Holy shit..." He rasps.
He should feel guilty.
But he feels too high to care right now. He tucks the soiled pink panties into his pocket.