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It didn't take long for Izuku and Shouto to realize they were after the same thing.
It starts towards the end of their third year—as they start looking towards the future, it's impossible not to think about all aspects of their future. Of course, Izuku would be lying if he said he hadn't had this in his mind since he presented as an alpha and Kacchan as an omega, but it isn't until they're facing the rest of their lives that he realizes how much he wants Kacchan like that.
All things considered, maybe it wasn't the best idea to move in together after they graduated. Two alphas, both after the same omega, all living under the same roof. It should have been a recipe for disaster, and with any other group maybe it would be. But Izuku and Shouto weren't like regular alphas, and Katsuki was certainly unlike any other omega. And anyway, it wasn't that bad; occasionally Izuku or Shouto would get a whiff of Katsuki's uncensored smell, and they'll have to lock themselves in their rooms and furiously jerk off. Sometimes that just made it worse, though. Fucking into their hand instead of into Katsuki's tight hole. The desire left Izuku aching, sometimes.
Of course, it didn't help that the three of them were pretty much inseparable—living together and working together, Burnin' often joked that the three of them lived in each other's pockets.
"Don't you ever… I dunno, get sick of each other?” Ochaco asks. "I mean, I love Tsuyu, but there are some times when I just—well." She laughs self-consciously. "You seriously never feel like that?"
Izuku shrugs. "Not really." And he doesn't, truly. Sure, there are times when they get on each other's nerves—Katsuki especially, if he's being honest—but there was never a time when Izuku wanted less of them.
It started small, with Kacchan. They got close after the war. Close enough that it wasn't weird when Izuku started getting a little... touchy. A hand on Katsuki's back, an arm around his shoulder, and later, when he was a little more bold, a hand around Katsuki's wrist, fingers brushing against his scent gland. He was always trying to show off for Kacchan, especially as he got stronger; although depending on Katsuki's mood, sometimes he gets offended at the supposed implication that he couldn't move his own shit, or that he wasn't just as strong. It's a delicate balance between trying to court Kacchan and trying not to set him off—but Izuku wouldn't want it any other way.
He's not sure how long it took him to realize Shouto was also expressing interest in Katsuki. More likely, the better question would be when he couldn't ignore it anymore. When he couldn't turn a blind eye to it. Shouto wasn't as touchy or affectionate as Izuku was, so he showed his interest in different ways. At first Shouto was so atrocious in the kitchen that Izuku assumed it was a ploy, although Shouto later assured him it wasn't. Regardless, it ended up with cooking becoming their… thing. Izuku hated feeling the way he did, but sometimes it was hard not to feel left out when he could hear them together in the kitchen, in a world of their own.
He doesn't do anything about it though. He gives Shouto his space with Kacchan. Izuku has never been a stereotypical alpha; he's pretty sure everyone was surprised when he presented. He knows that it isn't… normal, necessarily, to stand aside and let another alpha pursue the omega he was interested in. And it isn't that Izuku doesn't feel jealousy or possessiveness over Kacchan. Any other person, alpha or not, who gets a little too friendly with Katsuki gets Izuku's hackles raised. It's just—different with Shouto. He doesn't know how else to explain it.
It’s a few months after they move in together that Izuku brings it up. Katsuki is out on patrol, and it's just Izuku and Shouto. They're watching TV and eating takeout, a bad habit they can only get away with when Katsuki isn't home for dinner. Eventually, Izuku turns the volume of the television down. "Hey, Shouto?"
After a pause, Shouto says, "Yeah?" Izuku has a feeling he knows where this is going. They just get each other like that.
"You want him too, don't you? Kacchan."
Shouto says, "Yes." Izuku lets this sit between them for a moment. It feels good to have it confirmed, spoken aloud. They've both been orbiting around Katsuki like he was the sun, pretending they weren’t both on the same path.
Finally Izuku says, "What do you want to do about it?"
Shouto thinks about this. "I don't want to give up. You don't either." It isn't a question; Shouto knows him.
"I don't want to lose you," Izuku says. It's very important to him that Shouto knows that no matter how much he wants Katsuki, it isn't worth losing Shouto over.
Shouto nods. "Me neither. We have to agree that no matter who he chooses—"
"We won't let it change you and me," Izuku says, eagerly finishing the thought. He holds out his pinky, and after a moment of looking at it, Shouto links his with it. They pinky swear that night, and Izuku knows neither of them will break it. If it were anyone else, any other alpha, Izuku doesn't think he could do it. He doesn't think he could handle seeing Kacchan with someone else. But if it's Shouto—he doesn't fully understand it, but he knows that it's okay if it's Shouto.
And ever since that day they've kept their word. More than that—they help each other, leave time for the other to be with Katsuki, cover their shifts so they can take him on poorly disguised dates. Both of them are too afraid to push it farther, to put it into words, to actually ask Kacchan. Maybe they're afraid of rejection—or maybe it's acceptance they fear. Anything that would end the limbo they're in with all three of them on equal footing. An answer means someone is pushed out.
Izuku wants Katsuki; he wants him so much sometimes he feels dizzy with it. But maybe there's a part of him that wants Shouto too—or at least, that doesn't want what they have to change. So even as the two of them get more and more obvious, they never make any move to make it anything more. Even as Katsuki walks around their apartment in Izuku's shirt and Shouto's sweater, their scents mingling—they don't say anything. Honestly, Izuku likes the way their scents combine. He thinks he might like it more than just his and Kacchan's scents. It feels unfinished without Shouto; Izuku doesn't know what that means.
Who even knows how long it would have continued like that, stagnant, if it hadn't been for the villain fight. It started out normal enough—but then the villain gets into a physical fight with Katsuki, and at some point during it, Katsuki's scent patches get ripped off. They're in a narrow alleyway, and the tantalizing scent of spice and smoke flood the space. All three of them—Izuku, Shouto, and the villain—all stop, nostrils flaring. The villain reacts first; neither Izuku nor Shouto will ever forgive themselves for the way Katsuki's scent made them freeze.
"Oh, don't you smell good,” he says, licking his lips like a cartoon pervert. Alpha pheromones mix with Katsuki's scent, muddying it. Izuku doesn't realize he's growling until he realizes Shouto is also growling. Both of them still have their scent patches on, but the anger and possessiveness is so powerful that their patches cannot fully contain it. It spreads through the alley, thick and cloying, and both Izuku's and Shouto's scent is shouting the same thing— ours. Ours. Ours.
And then there's a giant blast, and the villain flies backwards into a building. He hits his head and then slumps unconscious to the ground. "This is Dynamight,” Katsuki says into his comm. "I'm sending you a location. You'll find the villain there. Deku, Shouto and I need to disengage."
"Do you need medics?" Izuku hears in his ear.
"No," Katsuki says. "Just send someone to pick up this loser." They’ll have to come up with a reason why they had to leave, but that’s a problem for later. Izuku doesn’t like pulling the Todoroki card, but sometimes it is handy that Shouto is the son of the boss.
After that Katsuki turns the full weight of his glare on Izuku and Shouto, who shrink back at the unimpeded anger that's bursting out of him. "Tie him up," he orders. “Then we're going home. I've had enough of this."
Izuku and Shouto follow Katsuki home, feeling a little like criminals walking to the gallows. Katsuki doesn't speak on the way back, so Shouto and Izuku stay quiet, too, occasionally shooting each other a look. The two of them are experts at understanding each other, so they don't need to speak to get the point across: Katsuki is pissed. They'd crossed a line; they'd fucked up.
Katsuki had been adamant since the day he'd presented as an omega that it wouldn't interfere with his hero work or his quest to be number one. And for the most part it didn't—omega heroes were getting less rare, and the one time a reporter had asked Kacchan when he was planning on settling down and getting pregnant, he'd taken her microphone and blown it up. After that, there weren't a lot of people brave or stupid enough to say those kinds of things to Katsuki at all, or indeed anything pertaining to his secondary gender. Izuku knows how much of an uphill battle being an omega hero can be. He's always tried not to add to that trouble. But now—this wasn't as bad as it could have been, since it had just been one villain who'd be locked up in jail soon. But if it hadn't just been the one villain—if they had been in a more public place, or if they had been surrounded by different heroes and civilians, the way Izuku and Shouto reacted would have had dire consequences for Katsuki. Even though he had been the one to ultimately take down the villain, even though he was more than capable of taking care of himself, that wouldn't matter. All people would see would be two alpha heroes growling and sending out pheromones like that dirty, narrow alley had been their den. Two alphas set off. Izuku has seen it time and again, and even if it's less common now that doesn't mean it's not a widespread problem still. People saying omega heroes were a distraction . That they'd endanger more lives than they saved. That they should stay at home and raise their pups and leave the hero work to the alphas and betas.
Izuku knows this is bullshit, and he knows placing all the blame on omegas makes them a convenient scapegoat. But it wasn't Katsuki's fault Shouto and him acted like that today, it's theirs. They should be able to control themselves.
The three of them get home; Katsuki orders them to sit on the couch and they do, sides touching for support. Izuku wonders if Shouto is thinking the same thing he is—did they ruin this for good?
Katsuki stands in front of them and stares the two of them down, arms crossed. He glares at each of them in turn, and then he sighs. "Okay, listen. If we're gonna do this it's time to set some fucking ground rules. The first is that if either of you do that again, I'll rip your dicks off and knot you bastards with them."
Izuku does not mention that once their dicks were ripped off, they wouldn't be able to pop a knot. He doesn't think Katsuki is going for realism. "That's... fair," Izuku says, because it is, after what they did. "But Kacchan... you said ‘if we're going to do this’. What is 'this'? what are we doing?" There's only one answer he can think of, but he's afraid it might just be wishful thinking.
Kacchan rolls his eyes. "I'm not an idiot, I know you assholes have been courting me since graduation. Was waiting for one of you to grow a goddamn spine instead of just cooking me shit or shoving clothes at me, but apparently that's not going to happen." Izuku and Shouto exchange glances. "But what we're not gonna fucken do is act all jealous and pissy because some creep makes a comment. I can handle my goddamn self. Are we clear?"
Sufficiently scolded, Izuku and Shouto nod. "Yes, Kacchan."
"Sorry," Shouto says. Katsuki rolls his eyes and walks over to the couch, and then he makes a motion indicating he wants Izuku and Shouto to move apart. When they do, he settles in beside them, taking out his phone. Izuku and Shouto exchange looks over his head, and when Katsuki still doesn't say anything, Izuku tentatively says, "Um, Kacchan?”
Katsuki grunts but does not otherwise say anything. "Well, it's just... you didn't tell us who you're, um... choosing."
Will it be Izuku, with all their history and baggage, with the scars on their bodies from hits taken to protect the other, with pictures of the two of them already on display at their mothers’ houses? Or will it be Shouto, with his pretty face and soft voice, a boy who wandered into their lives accidentally and set up a home there, a boy just as loved and important even without the fifteen odd years Izuku and Katsuki had with each other. Shouto would be a wonderful choice for an alpha, for a mate. A perfect alpha for an omega as perfect as Kacchan.
Izuku or Shouto? Shouto or Izuku? Izuku should be looking at Katsuki while they wait for an answer, but he can't tear his eyes away from Shouto. He's not sure which name he'd rather hear, his or Shouto’s. It's not that he doesn't want Katsuki—it's that he doesn't want to lose Shouto. Even with their pinky swear, even if they stay friends, the shape of the three of them will change for good, and someone will always be on the outside looking in. Izuku doesn't want that for himself—but he doesn't want it for Shouto, either. Izuku keeps looking at Shouto, and Shouto keeps looking at him. So it's Shouto's reaction that Izuku sees first when Katsuki says, "Hah? I ain't choosing."
Izuku watches as Shouto's eyebrows furrow together, and he sees the briefest spark of hope flit across Shouto's features before he tamps it down. Izuku feels the same—because surely Kacchan doesn't mean what he thinks he means?
"Wait, what?" Izuku asks, finally looking away from Shouto to study Katsuki instead, who is still playing around on his phone, the perfect picture of indifference.
"You both want me, right?" Katsuki asks, but he doesn't wait for an answer. "So then why the hell do I have to choose?"
Izuku is barely breathing, so afraid of doing anything that might break this, or cause him to wake up from the greatest dream of his life, or something. He just stays stock still, like Kacchan is one of those predators who can't see you if you're standing still.
“Are you… really, Kacchan?” Izuku can barely believe it; he looks back at Shouto, whose eyes are wide and shining.
“You fucken deaf or something? I don’t repeat myself.”
Sunshine blooms in Izuku’s chest, and he laughs, joy flooding through him. He puts his arms around Katsuki and squeezes.
“Kacchan is perfect,” he says; he pulls Katsuki up to his feet so he can hug him properly, still laughing, still reeling at the fact that he’s getting everything he wants. Katsuki and Shouto. He doesn’t have to lose either of them.
“Yeah, I am,” Katsuki responds. “And that means I deserve two alphas.”
What a perfect, wonderful omega they had.
That they had. Izuku pulls away from Katsuki and looks back at Shouto on the couch, who is staring at him with that soul piercing expression. Izuku steps forward and kneels on the couch, hand coming up to gently cup the side of Shouto’s face with his scar and leaning forward to kiss him. His lips are soft, and they curl up slightly at the edges. He’s smiling, Izuku realizes. Smiling into the kiss.
Izuku doesn’t get to revel in this for long, because the two of them are forcibly ripped apart.
"Oi!” Katsuki shouts. “The fuck do you two think you are, kissing each other first! Stupid shitty alphas!"
Katsuki is beyond annoyed at the two of them—but his words flip a switch, and suddenly Izuku and Shouto have eyes only for him. Izuku is the first one to reach out, to pull Katsuki into his lap and claim his mouth, hands spread out over his back as they kiss. He’s wearing one of Shouto’s shirts, and the smell of them is so good it has Izuku literally drooling. How perfect they both were; how lucky Izuku was to have them.
“I’m sorry, Kacchan,” Izuku says into their kiss. “You have all our attention, now.”
“Hmph,” Katsuki says, even as he wraps an arm around Izuku’s neck and moves closer. Izuku has his eyes open—he’s waited too long for this moment not to memorize the exact way Kacchan looks when he’s kissing him—so he sees the way Katsuki’s other arm reaches out across the couch, the way his fingers grasp at Shouto, snagging a hold of his shirt and tugging. He and Izuku pull away from each other, and as Katsuki turns his head to kiss Shouto, Izuku leans forward to press his lips to the elegant stretch of Kacchan’s neck, lips and tongue and teeth teasing the spot right below his scent gland. It has Katsuki panting and writhing on his lap, the occasional whine he’s unable to stifle lost to Shouto’s kiss. He still doesn’t have scent patches on, so Izuku and Shouto get the full weight of him, the anticipation and desire clouding his scent, the message he’s blasting through their entire apartment— fuck me, fuck me, fuck me.
And God, Izuku wants to. He’s already hard in his pants, and he can tell from the way Shouto grips Katsuki’s hip, fingers curled like claws, that he’s feeling the same. Izuku’s only sexual experience was the time he’d had to kiss Tokoyami in third year during a game of spin the bottle, and that—well, it doesn’t give him much to draw on, all things considered. Izuku has never really considered sex a big part of his life, other than jerking off, which was almost more of a chore than anything else, a reminder that he only had his hand and not Katsuki. But now, with a willing omega in his lap and another alpha beside him, Izuku’s hornier than he’s ever been. Suddenly he understands every shitty public sex porno where the alpha and omega can’t even wait until they’re home to fuck. Izuku wants to swoop Katsuki up and take him to his den and fuck him and knot him until he can’t remember his own goddamn name, and then he wants to sit back and watch Shouto do the same.
He pulls back. He has to, he’s going to lose it if he doesn’t. Shouto does, too, when he feels Izuku move, and Izuku wonders how he’d ever planned to do this without him. Shouto is just as much a part of him as Katsuki is.
Katsuki tries to chase Shouto’s lips when he pulls away, eyes opening to look at him in confusion and annoyance when Shouto moves out of range.
“Kacchan,” Izuku says; he can see the subtle flaring of Shouto’s nostrils. “Kacchan, wait.”
“ Why,” Katsuki says unhappily. He grinds on Izuku’s lap and he brings his hands to grip Kacchan’s hips, trying to keep him still before Izuku comes in his pants like a virgin (he is, but that’s not the point).
“Slow down,” Shouto says. Izuku can feel how difficult it is for him to say the words, can feel the tension in his muscles and the ache inside him. “We don’t want to rush.”
“We’re gonna do this properly,” Izuku says. He runs a soothing hand up Katsuki’s back, who is bristling on Izuku’s lap like an angry cat.
“And who the fuck decides what’s proper?” Katsuki says. His fingers cup Izuku’s neck, finding the edge of his scent patch and ripping it off. Then he turns to Shouto and does the same—and then the truth is undeniable, their scents mixing and spreading through the living room. Katsuki leans back, resting his hands on Izuku’s knees, arching his back and craning his neck. Izuku is so hard he’s at risk of bursting through his pants. Katsuki is so fucking pretty, and Izuku’s self-control is fading fast. If Kacchan wanted them to touch him—if they all wanted it now, why should they have to wait?
Izuku has never wanted anyone else. Nothing has ever felt as right as the three of them together.
“Fuck that,” Katsuki says, eyes sliding between Izuku and Shouto. “I want to be fucked,” he says bluntly. “If neither of you wanna do it I’ll find an alpha who will.”
Katsuki must have known how they would both react to that, especially after what happened in the alley earlier. Shouto grabs him and drags him between his legs, back against Shouto’s chest as Shouto grinds his hips up into his ass, teeth clamped down on his shoulder. Izuku reaches for the hem of Katsuki’s pants, ready to tear them off him and knot him on the couch, but then Katsuki says, “Wait.”
Both of them still; Shouto removes his teeth from Katsuki’s shoulder like a dog caught chewing something he wasn’t supposed to. But all Katsuki says is, “Not on this fucking couch, let’s go to my room.”
Izuku and Shouto lock eyes. Neither of them have ever been in Katsuki’s room, of course, although Izuku will admit to sometimes stopping outside the door and trying to get a whiff beyond the neutralizers.
“Are you sure?” Shouto asks.
“What’d I say about repeating myself?”
If Katsuki isn’t second guessing himself, Izuku isn’t going to second guess him either. He stands up swiftly and hauls Katsuki to his feet, Shouto following quickly like he’s being pulled by a magnetic force.
There’s no nest, although Izuku isn’t surprised. Katsuki only nests when he’s on his heats (or at least, Izuku is assuming—that’s when he’s noticed a large number of his clothes going missing, at least). But the smell— it’s a part of everything, there’s not a single part of the room that isn’t infused with Kacchan’s scent, the one place he never has to hide, never has to wear blockers. Shouto reels back when it reaches him like he’s been physically hit, and Izuku reaches out to him, grabs his hand and squeezes. They’re here and they’re together.
Katsuki saunters in and starts undressing, pulling his pants off and stepping out of them, then the top of his uniform, letting it drop to the floor, then his underwear, like a trail of breadcrumbs to his bed for the two of them to follow. Shouto shuts the door, neither of them capable of taking their eyes off of Katsuki, who has climbed onto his bed and lays in the middle, propped up on his elbows as he looks at his two dazed alphas.
“You two just gonna fucking stand there?” Katsuki asks. “Fuck, how’d I get such useless alphas—”
And that’s a challenge if ever there was one, and both Izuku and Shouto rise to meet it. They need to, Izuku has to show Kacchan that he’s wrong, that he’s not a useless alpha, he’s good, the best, he’ll take care of him—
God, Izuku wasn’t even in rut and he feels like he’s going to go insane with need. He practically stumbles over his feet to get to the bed, clumsily taking off his clothes—Shouto is struggling with the zippers on his uniform, hands shaking, in eagerness or anxiety Izuku isn’t sure, so he gently pushes his hands aside and helps him with it, kissing him as he does.
When they’re naked they both climb onto the bed; Izuku thinks about Shouto’s shaking hands and puts a hand on his back, pushes him forward onto Katsuki so he can crawl on top of him and kiss him, skin sliding against skin. Not giving him any time to think, to doubt. Shouto grinds down against him and Izuku reaches out to grab Katsuki’s hand, taking each of his fingers into his mouth in turn before he runs his mouth along his inner wrist and across his scent gland. It has Katsuki making another one of those noises that Shouto eagerly swallows, hiking one of Katsuki’s legs up around his waist.
Sooner than Izuku might have thought, Shouto pulls back. Again, Katsuki does the thing where he tries to chase after him to prolong the kiss—it’s really cute.
Shouto looks at Izuku. Even without a heat or rut, the pheromones that the three of them are pumping out have Shouto’s pupil’s black as night, and Izuku can feel his fangs threatening. Kacchan is driving them insane—no, not just Kacchan. They’re driving each other insane, too, Shouto and his delectable smell and his salty kiss and soft voice and unwavering presence in Izuku’s life.
“How do you wanna do this,” Shouto says, and his voice is raw, deep and hoarse like it’s been scraped over rocks, and God, if Izuku had known it was going to be like this he would have confessed to Kacchan ages ago.
“I want one of you to knot me,” Katsuki says, in a voice Izuku is forced to call petulant.
“I know,” Shouto says, running a hand down Katsuki’s leg to soothe him. “I meant who’s doing it first.”
A good question. Izuku looks between the two of them. Maybe he should be selfless and offer to let Shouto go first—but there’s a part of his brain that he’s trying his best to ignore that’s absolutely screaming at him to claim his omega, to be the first.
“You should go first,” Shouto says, a better person than Izuku. “You two have known each other longer.”
Izuku shakes his head. “No, I don’t want to start this like that, by putting emphasis on that, because it’ll never be fair to you. You’ll never catch up, it’s not fair.”
“Can one of you assholes just put your fucking dick in me!” Kacchan does not care about their moral dilemma. He’s upset, and Shouto jumps into action, making the decision and moving quickly to soothe their agitated omega. He lays down beside Katsuki and slides an arm under his head, pressing a kiss to his temple as he uses his legs to trap one of Katsuki’s and spread them. With his free hand he dips his fingers between Katsuki’s legs, coating them in the copious amounts of slick Kacchan has produced already, using that to help as he wraps a hand around Katsuki’s cock and jerks him off.
Shouto turns his gaze on Izuku. “Fuck him, Izuku,” he says, and Izuku doesn’t know which part of that sentence he likes more, the swear or his given name on Shouto’s tongue. “He’s wet for you. I want to see you be the first.”
Izuku can’t argue against that. He’s not strong enough to put up even a token resistance for Shouto to be the one. Instead he lunges forward and kisses Katsuki, tongue shoving into his mouth harsh and messy and possessive in the way it tries to claim every inch of Katsuki’s mouth. As he kisses him he shoves two fingers into his hole. Shouto was right; he’s wet, he’s really wet, making an obscene noise with each thrust of Izuku’s fingers inside him, and now it’s Izuku’s turn to feel those whines against his lips as he opens Katsuki up for him.
“Are you okay, Kacchan?” He pulls back to ask, even as he continues to finger him, another finger easily sliding into him. “You’ll tell us if you want us to stop?”
“If I want you to stop you’ll fucking know,” Katsuki says, hips jerking up into Shouto’s fist and down onto Izuku’s fingers. “Fuck, Izuku, come on, stop teasing—”
He hadn’t meant to tease, he’d only meant to make sure Kacchan was ready. He pulls his fingers back, dripping slick down to his wrist that he uses to coat his dick before he lines himself up with Katsuki’s hole. He’s trying to decide if he should go slow or fast and get it over with when Katsuki shoves himself down in one go.
“Kacchan,” Izuku lets out a strangled cry as he watches his cock disappear into the plush warmth of Kacchan’s ass. His hands search frantically for something to grab onto, to center himself before he comes just from putting it in, and he settles by grabbing Katsuki’s hip with one hand, and Shouto’s hand with his other. Shouto squeezes his fingers, the same steady comfort that Izuku is to him.
“Does it feel good, Katsuki?” Shouto asks, and even though it sounds like he’s checking in, it also sounds like a command, and Katsuki’s eyes seek him out desperately. “Tell me.”
“ Yes,” Katsuki says, as Izuku pulls out and fucks back in. He wants to go slow and work up to it, get Kacchan used to it, but with each thrust into him he finds himself going a little faster, seeking out that wet heat with a single minded focus that has his hips shoving against Katsuki’s with the damning sound of skin on skin. All the while Shouto is whispering into Katsuki’s ear, and although Izuku can’t hear what exactly he’s saying he can see the way Katsuki reacts to it, the moans and whines and frantic nods.
Izuku is hit with a sudden need, and he pulls out. “Roll over,” he says, and although he hadn’t said it as a command Kacchan listens as if it had been one, scrambling onto his stomach with his ass in the air like a proper little omega whore, sloppy hole on display and cock hanging heavy between his legs. Shouto keeps touching him, running his hands over his back and petting through his hair as Izuku shoves back inside him, and he’s a little louder now, telling Katsuki how good he was, taking Izuku like this. How perfect he is. The best.
“Shouto,” Izuku says through clenched teeth, “make him come.” Shouto’s hand returns to Katsuki’s hard cock and his whispered words get a little more frantic and a little more dirty until Kacchan comes spilling onto the sheets. Izuku closes his eyes and grips Katsuki’s hips and just lets himself fuck, lets himself chase his release, using his omega the way he was meant to be used, until his knot catches and he comes hard, fingers digging bruises into Katsuki’s skin as he fucks him full of cum. Katsuki moans as Izuku fills him, so fucking tight around his dick. Izuku carefully falls to the side, spooning around Kacchan and trying not to jostle him too much from where he’s still securely milking Izuku’s knot. Izuku noses at his hairline as Shouto rearranges himself on the other side so Katsuki is safe between the two of them. Two alphas was a great idea, a part of his brain tells him. No one will be able to get his omega now.
“You’re amazing, Kacchan,” Izuku tells him softly. “I’m so glad we didn’t wait.”
“Told you,” Katsuki says, voice a little weak but still firm with his usual condescension. “I dunno who you’re trying to fool, you wanna get hitched in a church or something?”
Izuku giggles and runs a hand over Katsuki’s stomach, full of Izuku’s cum. “Are you bringing up marriage already, Kacchan?”
Katsuki elbows him, and Izuku lets out an oof and naturally moves away, which tugs at where his knot is still—
“ Ow, shitty Deku! The fuck are you doing!”
“You’re the one who elbowed me, Kacchan!”
“Lie down and be still,” Shouto says firmly, and the two of them stop and move back together so Katsuki is no longer in pain. Izuku gives him a placating kiss to his scent gland and then reaches out to squeeze Shouto’s hip.
“Shouto,” Katsuki says. “You’re next. Still want your knot, too.”
Izuku’s dick twitches at the thought and Katsuki turns his head slightly to glare at him, as if warning him not to get going again.
“Are you sure?” Shouto asks. “You’re not on your heat, I don’t want to push you.”
Izuku is able to slip out of Kacchan now, and he carefully pulls out and separates them.
“I already told you,” Katsuki says peevishly.
“I want to make sure—”
Katsuki shoves Shouto onto his back and climbs on top of him swiftly, grinding against Shouto’s erection and coating it in a mixture of his slick and Izuku’s cum before he lifts his ass and then sits on Shouto’s cock, taking it down to the hilt in one smooth movement just like he’d done with Izuku. Shouto cries out, a strangled sound unlike any Izuku has heard before. He wants to hear it again. He kisses at Shouto’s chest and shoulders and neck and jaw as Kacchan rides him, Shouto gripping one of Izuku’s hands with his own hand—which, Izuku notes, is steadily rising in warmth. He’ll keep holding on until he has to let go.
“Doesn’t he feel amazing, Shou?” He says into Shouto’s ear. “He takes you so well. He looks so good on top of you. Does he feel good?”
“Izuku,” Shouto moans, and Izuku kisses him, even though all Shouto really has the presence of mind to do is open his mouth and let Izuku do what he wants. All the while Katsuki is still bouncing on his lap, taking Shouto’s dick again and again until his knot swells—Katsuki leans forward and rides the knot, working his hips so it pops in and out of his hole in the single sexiest and most obscene thing Izuku has ever seen. He wonders where the hell he learned to do that.
When Shouto’s knot catches Katsuki grinds down on it, keeping that up even as Shouto comes and shouts and jerks until Katsuki comes again, too, cum dribbling out of his dick as he’s filled for the second time. He’s shaking by the end of it, and Izuku helps guide him forward to lie against Shouto’s chest. Shouto’s arms rise to wrap around him, a natural instinct more than anything, since he seems to still be coming inside of Katsuki. Izuku hugs them both, telling them how wonderful they both are, each word more truthful than the last.
Katsuki seems to doze off—or at least, he appears to wake up suddenly, trying to roll off of Shouto and yelping when the knot tugs. Izuku grabs him and pulls him back. The sex had gone surprisingly smoothly, but apparently they were going to have to get used to being knotted together.
“Stay, Kacchan,” Izuku says softly. “We’ve got you.”
Katsuki doesn’t give his usual response to this (“fuck you”) which is a testament to how fucked out he is. Izuku watches him with a smile on his face, looking between him and Shouto, who looks like he’s also falling asleep.
Izuku decides to ask. “Kacchan… if you knew, why didn’t you say anything?” Certainly tradition said that omegas were to be pursued and not the pursuer, but Izuku can’t name one singular time Katsuki has ever given a single fuck about that.
Katsuki is still nestled between them, dozing off against Shouto’s chest. He gives a kind of half-shrug. “Liked it,” he admits (note to self, Izuku thinks: Kacchan gets cute and pliable after sex). “Liked having two alphas fighting over me. Plus I didn’t want to let you two get away with being cowards.” He adds this as an aftermath, and Izuku has a feeling his initial reason was the more truthful of them. Katsuki was proud and liked being the best, and no doubt his omega was positively preening over Izuku and Shouto falling over each other to prove themselves worthy of him.
He grins and kisses Katsuki on the head, and it’s only when they’ve all settled back into a pile that he hears it.
“Kacchan… are you—”
“Purring,” Shouto finishes. “You’re purring.”
“No I’m fucking not!” It’s an automatic denial, but it’s pointless, because he is. They can both hear it in the quiet of his bedroom. A smile plays at Shouto’s lips. “Fuck both of you!”
“You just did,” Izuku says, giggling more at the deeply incensed look Kacchan gives him than his bad joke. Katsuki scowls and tries to move off Shouto, who’s knot still hasn’t deflated, and Katsuki lets out a grunt of pain before he glares down at Shouto.
“How long’s it take your stupid knot to go down?” He crosses his arms and glares down at Shouto, and it’s such a ridiculous image considering he’s sitting on Shouto’s cock and Shouto is covered in cum. Izuku feels so full of love he might burst.
“I don’t know,” Shouto says with the patient tone of voice that always seemed to make Kacchan so mad. “I’ve never done this before.”
Katsuki makes a frustrated noise before he slumps back down on Shouto’s chest. “Fuck you, Icyhot. Why’re you always such a goddamn overachiever?”
“I’m going to take that as a compliment.”
“Fuck you, it wasn’t one.”
“Hey,” Izuku says. “I’m really happy right now.”
Both of them look at him. Shouto’s face is soft, and Izuku knows he’s feeling the exact same influx of feelings that Izuku is.
“Don’t be stupid, Izuku,” Kacchan says, but then he reaches out a hand and says, “Come here.” Izuku moves in to kiss him; Katsuki rubs his fingers in the oil of his scent gland and smears it on his lips, and then he bends down to kiss Shouto, who eagerly laps up the both of them. Then he pulls back and puts his head on Shouto’s chest, closing his eyes. “Wake me up when your stupid knot goes down,” he mutters. Shouto smooths a hand over his hair, and Izuku may or may not use Fa Jin to get to the other side of the room and back to turn off the light really quickly. He’ll never say. You have no proof. It’s just that he has a feeling they’re not going to be leaving this room for a very long time—for anything except water and food, of course. So best to let Kacchan get some sleep in. Izuku plans to keep them both up tonight.