As a child, Izuku was a rising sun. A constant in Katsuki’s life that never possessed any particular talents, though he could always count on him to show up on time.
He liked being around Izuku because Izuku loved being around him. He would teach him how to do new things, and Katsuki would make it his mission to become better at them than the older boy in stupidly short amounts of time. Katsuki liked Izuku because Izuku never got upset when he did that—never stopped teaching him.
Normally, Izuku was a kind and soft-spoken boy, but as years passed by Katsuki had learned how to bring him out of his shell. He knew just what to do to make him jump up and down in excitement, or how to motivate him, or anything else, really. He had a refined and nuanced understanding of Izuku’s control system. He knew exactly which buttons to press at any given time.
When Katsuki was seven, Izuku was twelve, and it was around this time that he became his babysitter, because while he couldn’t do shit if Katsuki were to injure himself, he was just tall enough to reach the microwave to heat up leftovers.
The five years that followed were a period of wholesome fun. Katsuki could still remember the way the boy used to wash his hair for him. That time when Katsuki yelled tsunami and splashed Izuku with soapy bath water one too many times, and the boy responded by shouting hurricane as he suddenly turned on the shower head. Hey Deku, do you wanna fucking die? He’d laughed.
Prior to the age of thirteen or so, if Katsuki had to describe Izuku’s features in one word, that word would be soft. Izuku had been a soft, sunshine child, who eventually grew to be a soft, sunshine teenager, who then became something else just as soft, just as sunshine-y. Something Katsuki could only acknowledge as being ‘an adult’ in a distant, nebulous sense. It just wasn’t the same, because it was Izuku.
He’d never paid all that much attention to Izuku’s appearance beyond just a vague understanding of it as something aesthetically pleasing. And then, of course, puberty happened.
Years passed by in a haze of arousal as Izuku played a starring role in all of Katsuki’s fantasies. Izuku became his tutor, and it had become standard procedure for Katsuki to have to suppress the urge to just bend him over whatever object he was adjacent to and fuck him until he cried. Every encounter was a battle for him, and his only consolation was that he didn’t seem to be alone.
You see, Katsuki always knew that Izuku belonged to him, deep down. He was just waiting for Izuku to accept it. But he was done waiting. He couldn’t take it anymore, and so, Katsuki adopted a simple but effective strategy to ruin Deku’s fucking life.
He had to ease into it. Had to be careful not to be too obvious about what he was doing, so he started with something seemingly innocuous: the black tank top. Except all the time.
There was no point in being modest about it: Katsuki had a great body. He was well aware of that fact, had watched it develop over the years; a culmination of all his hard work. So, the next time Izuku came over, Katsuki answered the door in sweatpants and a black tank top that hugged his body in all the right places. As he watched Izuku’s face light up a luminescent red, felt his eyes lingering on his broad chest, his biceps, his waist… Katsuki felt a deep sense of satisfaction.
But it wasn’t enough. He had to take it up a notch. And so, one hot summer day, at the age of seventeen, Katsuki yanks the front door open wearing nothing but a pair of dark sweatpants that hung low on his hips.
“‘Sup, Deku.” He greets casually, making a conscious effort to appear impassive as Izuku gapes at him.
“K-Kacchan,” he stutters, looking away before adding a belated, “Hey…”
Katsuki stares at him for a moment, allowing himself a subtle smirk while Izuku wasn’t looking. After a moment of standing in silence, he speaks up.
“Well, fuck, are you just gonna stand there?” He asks, pointedly holding the door open wider. “It’s hot as balls. Come in.”
“Ah, right…” Izuku replies, his eyes downcast as he follows him inside. As they ascend the stairs and walk down the hallway, Izuku seems to take notice of the absence of sound within the house. “Where are your parents?”
“Not here.” He states, intentionally vague, as he holds his bedroom door open for Izuku. It seemed like the older boy wanted to say something about it, but he held his tongue. As he enters the room, Katsuki follows and shuts the door behind him firmly, with a sort of finality that was only significant to him.
“So, what did you need help with?” Izuku asks, taking a seat in the extra chair by Katsuki’s desk, which had probably been there for years.
“Calculus,” he replies, sitting at the edge of his bed before collapsing onto his back. “‘Related rates’ is the worst thing that’s ever happened to me.”
“Oh, yeah. A lot of people struggle with that,” Izuku says. “It’s not so bad once you learn the procedure, though.”
“Fucking stellar.” Katsuki kicks his legs up in the air and flings himself back onto his feet, engaging his muscles far more than necessary for simply walking over to the desk. As he sits down in his office chair, he notices the way Izuku’s eyes follow his movements, fixating on his abs as well as the V of his hips. With a smirk he doesn’t even try to hide, he says, “Show me your secret, Deku.”
After around half an hour of practice, Katsuki had become restless. Even after all that time, Izuku didn’t seem any closer to getting used to his state of undress. Which was great for Katsuki, as it meant his plan was working. It was not, however, so great for Izuku, because it made Katsuki want to destroy him.
As he turns to meet Izuku’s eyes, his own linger fondly on his intense, ever-present blush. He watches the other open and close his mouth a couple of times before finally speaking up.
“Kacchan…” He swallows nervously. “Why are you, erm, shirtless?”
Oh good, Katsuki thinks, narrowing his eyes almost imperceptibly.
“It’s my house.” He replies, leaning in toward Izuku a bit. “I could be naked if I wanted to be.”
“Yeah, but…” Izuku’s eyebrow furrows. “You’re not usually shirtless, so…?”
“It’s hot as fuck, Deku.”
“Not really, though?” His eyes keep darting around the room. “It’s kind of hot outside, but it feels exactly the same inside.”
“Well, I’m fucking hot, Deku.” Katsuki smirks at the way the others’ eyes go wide. “What, does that bother you?”
“Ye—“ Izuku starts to say, but catches himself, and oh god, this is just too fucking good. “N-No, of course not… I just—“
“Hm, are you sure about that?” Katsuki purrs, rolling his chair closer to Izuku. Making their knees touch.
“Ye-Yeah, it’s—“ The older boy turns even redder, trying to look at anything but Katsuki. Well, that won’t fucking do, Katsuki thinks, licking his lips as he leans in closer. Until their faces are only about an inch apart.
Katsuki makes sure he can feel the warmth of his breath against his face as he rasps, “Deku…”
A high-pitched, involuntary noise comes from Izuku’s throat when he finally looks at the boy. As Katsuki’s eyes meet his, he sees his pretty green irises eclipsed almost entirely in black, and he fucking loses it.
He yanks Izuku toward him by the front of his shirt, making him stand as his lips crash against his. The older boy whines, tensing up only briefly before melting in his arms. Katsuki bites his lower lip harshly, makes him cry out as he invades his mouth with his tongue. It’s rough and messy and everything Katsuki has ever wanted.
Wasting no time, Katsuki shoves his knee between Izuku’s legs as his hands grab his hips. When he pulls him forward, making him grind against his knee, Izuku breaks away with a desperate, high-pitched moan. Upon realizing that the other was already half hard, Katsuki laughs, and while the older boy was too caught up in rutting his cock against his leg, he takes the opportunity to turn them around.
He shoves Izuku onto his bed, listens to him squeak as his back hits the sheets, and regards him like a predator hunting its prey.
“Did you think I wouldn’t notice, Deku?” He says, stalking around the bed slowly. “You think I wouldn’t notice you checking me out?”
As Izuku sits up on his elbows, Katsuki crawls onto the bed to shove him back down.
“You know how fucking hard it’s been? All these fucking years,” he grabs Izuku’s shoulders, nearly knocks the wind out of him as he shoves him into the mattress. “All these fucking years I’ve had to resist the urge to just rip off your clothes, bend you over and fuck your ass ’til you begged me to stop?”
“Ka-Kacchan,” He whimpered.
“So tell me, how the fuck—” He shoves his knee between Izuku’s legs again, making him cry out as he arches his back, “—am I supposed to resist it when you keep staring at me like you’re fucking gagging for it?”
“Kacchan,” He gasps, fingers digging into the sheets as his hips twitch up toward the other. “Kacchan, please—“
Katsuki smirks, grinding his knee roughly between his legs. He leans down, lets his lips brush the shell of Izuku’s ear as he speaks directly into it.
“Fucking hard already, Deku?” He whispers, nipping the shell of the older boy’s ear.
As Katsuki moves to situate himself between his legs, he grabs one of Izuku’s knees, hiking it up to his chest. Izuku’s other leg turns out, bending as it falls further open, and then Katsuki’s rolling his hips into him, and fuck, it’s so good.
“Oh, fuck yeah,” he groans, closing his eyes as he sits up. When he looks down at Izuku, at the way the force of his thrusts make him rock up the bed, he grins. “Feel that?” He pointedly grinds his cock against the curve of his ass and basks in the high-pitched whine he elicits. “Mm, you want it, don’t you, Deku?”
His fingers trail under the older boys shirt, scrunching it up beneath his armpits as he begins toying with his nipples. Izuku gasps when his blunt fingernails drag across the sensitive flesh. Quickly, Katsuki discards the older boy’s bunched up shirt, returning to his task as soon as he has Izuku’s chest bare. When he harshly rakes those nails down his ribs, Izuku downright moans, his hips lifting off the mattress of their own accord, as if silently begging Katsuki to take his pants off.
“God,” Katsuki scoffs, palming the old boy’s cock roughly through his pants. “You’re just a fucking whore, aren’t you? A desperate fucking slut.”
“N-No!” He replies hastily, but Katsuki felt the way his cock twitched in his pants as those words left his lips. You’re not fooling anyone, Deku.
“Is that so?” He grins, shifting both Izuku’s knees over his shoulders as he leans in, grinding into his ass, slow and hard. “Hey Deku, remember how you used to tuck me into this bed?” He asks, staring directly into his eyes, their faces barely and inch apart. When Izuku tries to turn away, Katsuki grabs his cheeks and pulls him back. “Fucking look at me when I talk to you.”
Slowly, Katsuki begins working at the buttons on his pants, popping them open before dragging down the zipper. Izuku whines when he feels his fingertips dipping beneath the waistband.
“Remember how you used to read me bedtime stories here?” Katsuki asks, as he starts pulling the pants off of his hips. “Remember that time you fell asleep right next to me, halfway through The Lorax?” He laughs, pausing to lean back slightly, admiring the flesh as it was revealed to him. Izuku’s legs were so soft.
Katsuki tosses the jeans off somewhere behind himself. His hands sweep over Izuku’s smooth legs, dipping into his inner thighs as he forces the older boy’s legs further open. His erection is plainly visible through his boxer briefs, precum darkening the grey fabric around his tip. Slowly, Katsuki starts to rub him through the material.
“So many memories, Deku.” He states absently, transfixed by the sight of the older boy’s cock jumping at his touch. Losing patience, Katsuki lowers the elastic of his underwear, throwing the soiled garment in the same direction of his pants.
Katsuki sits back on his haunches, allowing the older boy’s legs to remain limply slung over his shoulders. He stares at the sight before him: Izuku, his childhood friend, his babysitter, his tutor—his everything, really—laid bare before him, skin flushed from his cheeks down to his chest. His nipples hard, his stomach rising and falling quickly with his breathing. Katsuki’s eyes trail further down to his hips. Izuku’s swollen, hard cock, already leaking for him.Izuku’s soft, full ass, spread open wide and inviting for him.
He didn’t even realize he’d been rubbing his own cock through his thin sweatpants until a high-pitched whine from Izuku’s throat broke him out of his reverie.
“So tell me, Deku. Even back then, did you know?” He asks, tugging at the drawstring of his sweats. He dips his fingers beneath his waistband, maintaining eye contact with Izuku as he slowly drags it down, freeing his hard cock. Katsuki held himself at the base, stroking a few times as he leaned in closer. “Did you know that one day you’d be lying in this very same bed, spread out and bare, while that same boy you used to take such good care of fucks you into the mattress?”
“Kacchan, ahh—“ He moans, lifting his hips off the bed, searching for friction.
“Beg for it.” Katsuki commands, rubbing his thumb over his tip.
“I said,” He leans down, rubbing the head of his cock between Izuku’s asscheeks. “Fucking beg for it, Deku.”
“I…” Izuku hesitates, his eyes bugging out and darting around anxiously. “I ca—“
“You want my cock, you’re gonna have to beg for it like the fucking whore you are, Deku.”
Izuku remains silent for a moment, words dying in his throat as his mouth moves uselessly. Katsuki begins to stroke his cock a bit quicker.
“I could always just get myself off like this, y’know.” He comments, leaning in and pressing his tip against Izuku’s entrance as he continues to stroke himself. “I could come all over your fucking hole and just leave you like this.”
This seems to spur Izuku into action.
“No!” He nearly sobs. “Please, Kacchan! P-Please…”
“Shh,” Katsuki says soothingly, sweeping Izuku’s bangs out of his face. “Come on, you know what you need to say…”
After a few seconds of hesitation, Izuku speaks again, his face burning hot and red.
“P-Please, Kacchan, I… I need it,” he starts off quietly. Casually, Katsuki reaches over to his bedside drawer, pulls a bottle of lube from inside and idly turns it in his hand.
“Please, I want your…” He chokes on the words. “Need your…” Izuku trails off inaudibly.
“Speak up, Deku,” Katsuki prompts, uncapping the bottle and slicking up his fingers. He circles the digits around his hole slowly at first, then abruptly shoves one in, making Izuku cry out noisily. “Speak up or I’ll make you speak up, Deku.” Katsuki wastes no time, starts working his index finger in and out of Izuku’s hole, reveling to his sweet moans and cries as they fill the air.
“K-Kacchan, please!” He wails. Katsuki adds another figure, rubbing at the older boy’s walls teasingly.
“Please what, Deku?” He thrusts his fingers inside roughly, feeling his cock throb painfully at the sight of Izuku’s hips rocking toward them, trying to fuck himself on his fingers. Katsuki adds a third.
“I need your—please, I just…” He squeezes his eyes shut as he swallows the drool accumulating in his mouth. Then, taking a deep breath, Izuku opens his eyes again, filled with tears as he looks up at Katsuki. Finally, he says, “Please, Kacchan… I need your, your cock—please, I need—I need you to fuck me, Kacchan. Please.”
Katsuki feels like he just won the lottery as he stares down at the older boy. His childhood friend, his former babysitter and current tutor, is lying beneath him, writhing on the sheets as Katsuki repeatedly buries his fingers inside of him, begging for his cock like his fucking life depends on it.
Slowly, his lips curl into a satisfied smirk.
“Alright, slutty Deku,” he replies, pulling his fingers out. He flashes his teeth at the noise of disappointment Izuku makes at the loss. “Since you asked so nicely, and all.”
Katsuki slicks himself up with lube, positioning his cock head against Izuku’s loosened hole. With the older boy’s legs still slung over his shoulders, he grabs ahold of his hips, his fingernails biting into his skin as he slowly pulls Izuku down. His back slips against the sheets as Katsuki drags him down the bed, mesmerized by the sight of his cock disappearing inside of the other as Izuku slowly takes every inch of him.
Once fully sheathed, Katsuki takes a deep breath and basks in the feeling of the older boy’s muscles clenching around him. Izuku moans, squirming against his hips, and Katsuki leans down to swallow some of those sounds in a deep, all-consuming kiss that leaves them both breathless when he finally pulls away, feeling the older boy’s muscles beginning to relax around him.
Slowly, Katsuki starts to pull out, watching the older’s muscles straining to release him. He pulls out until only the tip is left inside him, and when he shoves back inside, Izuku screams, wrapping his arms around his neck.
“Fuck—feel so fucking good,” Katsuki rasps, setting a careful, languid pace.
“Kacchan…” Izuku’s nails scratch down his back. “Ah! Kacchan!”
Katsuki smirks, resting his forehead against the older boy’s, offering no place for him to hide.
“You’re so fucking obvious, you know that?” He says, releasing a low chuckle as he grinds his hips into Izuku’s ass, making him gasp. “If you wanted it that bad, you should’ve just asked, y’know. What was it you always used to say when we were kids? ‘Use your words’?” He pulls out, shifting Izuku onto his side. Katsuki straddles one of his legs while holding the other against his chest as he snaps his hips forward again, enjoying the lewd sound of skin slapping against skin.
“What do you think your friends would say?” Katsuki asks suddenly, his fingers digging into the flesh of the older’s thigh. “What do you think they’d say if they knew you were letting the kid you used to babysit fuck your ass?”
“Kacchan!” He whines, cheeks flushing a dark red. “Don—“
“No, I wanna know.” Katsuki interjects loudly. “What do you think people would say if they could see you right now? Do you think they’d be surprised?”
Izuku bites his lips, closing his eyes.
“Mm, no?” He leans forward to speak directly into Izuku’s ear, forcing his leg further up his side. “Yeah, bet they wouldn’t be surprised at all. Fuck, Deku, just how long have you fucking wanted this?”
When he doesn’t reply, Katsuki stops moving. Izuku opens his eyes, looking mildly distressed.
“I asked you a fucking question.”
“It’s…” He trails off, averting his eyes. “It’s been, ahh—about two years…”
“No way,” Katsuki’s eyes went wide. “Two fucking years? Why the fuck didn’t you say anything?”
Izuku blinked, giving him a look. “Kacchan, two years ago, when you were fifteen, I was twenty.”
“Okay, that’s fair.” He stated flatly. “Still, two years I could’ve been fucking you? Hope you’re cool with not being able to walk after this. I’ve gotta make up for lost time.” He grins, pulling out of Izuku nice and slow before slamming back into him hard.
With that, Katsuki set a merciless pace, fast and rough and evidently perfect, if Izuku’s screaming is any indication.
“Kacchan! Kacchan, god, yes!” He cries out, scrambling to try and find something to hold onto. The position didn’t make it easy. Izuku’s hands go from grasping the sheets, to digging into his own hair, to finally settling on the pillow by his head. His fingers grip the soft material like a vice.
Katsuki leans down, tugging on Izuku’s earlobe with his teeth before moving on to his neck, biting and sucking marks in deep purples that adorn the older boy’s skin prettily.
As he works his neck, he snakes a hand down Izuku’s abdomen until he finds his cock, heavy, swollen, and leaking precum. He begins to stroke him, slowly at first, gradually working his way up to the speed of his hips.
Izuku’s a mess before him, crying out garbled versions of his name and words like ‘please’ and ‘yes’ and ‘more.’ He’s already a mess, and Katsuki only wants to mess him up further.
“You gonna cum for me, Deku?” He asks, biting the shell of Izuku’s ear as his hips continuously slam into his ass. “You gonna cum for your precious ‘Kacchan’?”’
Tears fill Izuku’s eyes. His bangs stick to his forehead, damp with sweat.
“Ple—Please,” He gasps, breathless. “Yes!” Izuku rocks his hips in no definitive direction. One moment he’s thrusting into Katsuki’s fist, the next he’s fucking himself back onto his cock.
“Do it, then.” Katsuki rasps. His lips brush against Izuku’s ear as he whispers, “Cum for me, Izuku.”
One more thrust is all it takes, and then Izuku’s tensing up, his leg twitching in Katsuki’s grasp as his walls spasm around him, and then he’s coating Katsuki’s hand with shot after shot of cum, screaming his name like it’s the only word he knows.
It doesn’t take much longer for Katsuki to follow him, losing it at the sight of the older boy coming undone for him.
“Nngh. Fuck, fuck, Deku—Izuku, fuck!” He grunts, groaning as he cums inside of him, his cock pulsing with each shot. He continues thrusting through his orgasm, fucking into the older boy feverishly until he can’t take it anymore.
He pulls out slowly, wincing at the overstimulation.
“Fuck.” He sighs, as he falls onto his back. “That was… fuck.”
“Yeah,” Izuku agrees breathlessly, his legs still shaking in the aftershocks.
They stay that way for a while, lying side by side, basking in the afterglow. After a couple of minutes, Izuku starts to stand up. Katsuki responds by immediately yanking him back down, manhandling the older boy until he had him straddling him.
“Wh—Kacchan, we still have to—the calculus, I—“
Katsuki rolls his eyes.
“I lied about being bad at related rates, dumb ass.”
For a moment, Izuku just stares at him. It’s like he’s debating whether or not he should lecture him. After a couple of seconds, he simply sighs.
“Well, there are other things I can teach you. Our session isn’t over, yet.” He reasons.
“Damn right our session isn’t over yet,” Katsuki nods. For a moment, Izuku seems relieved, but then Katsuki flips their positions, pinning the older boy under him once again with a mischievous grin. “What’d I say earlier? Gotta make up for lost time, Deku. It’s not over ’til you can’t walk,” he leans down, brushing his lips along Izuku’s slender neck.
“Kacchan, that’s not what I mea—ahhhh!” He moans, reaching up to bury his fingers in Katsuki’s hair.
And Katsuki kind of wants to laugh, but he doesn’t. Instead, he just spreads Izuku’s legs open a little wider, sucks on his neck a little harder, and loses himself in the pleasure of it all over again.