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primal instinct

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Kacchan has a love-hate relationship with the Alpha rut.


He hates how it owns him. Horny as shit for days. Wakes up grinding his hips against the sheets. Goes to sleep fucking into his own fist. Cock throbbing always until the dregs of arousal finally pass and he can become a functioning member of society again. Sometimes it’s a few days; that’s easy to handle. Sometimes it’s more like a week, and it’s his personal hell. Kacchan doesn’t like to give control to primal urges. Doesn’t like how they wreck him so thoroughly. Leave him craving and insatiable. He should be stronger than that, but you can’t fight with nature, apparently.


Fuck nature.




He does love the part where Deku gets involved. Where he lends a hand, mouth, or even more to get Katsuki through it. He’s not an Omega, despite how much of a pushover he can be, but he gets the job done. Lets Katsuki have his way with him however he needs to move past his basic instincts. Katsuki does the same for him when he goes into his own rut because that’s what a good partner does. He may be an asshole, but he’ll always reciprocate.


At least, for Deku, he will.


Why they got involved with each other, both Alphas, neither could say. Deku calls it love because he's a mushy gushy, lovey dovey asshole. Sweet as a sundae with a cherry on top. Katsuki calls it fighting the system. Fighting against what’s expected. Or maybe Katsuki is just horny all the time. Who knows?


What he does know is that Deku is always willing and wanting. Always ready to be bent over and taken as if he was some kind of submissive, good boy Omega. Good thing too, because due to some unfortunate, or maybe actually really fortunate timing, they both hit the rut at the same time. After fucking for who knows how many years now, that had never happened. Guess there’s a first time for everything.


The day starts wild, both waking up sniffing the air and immediately snarling at each other, deep and intimidating. Hackles raised and dull canines bared in some shitty display of dominance. Katsuki didn’t need to tell Deku he would lose. No one dominates Bakugou Katsuki without permission.


Deku loses, as expected.


The strong stench of Alpha pheromones more than doubled what usually fills their bedroom. It was dizzying and mouthwatering. Intoxicating. Katsuki licks his chops while straddling Izuku’s hips, pinning him down and running his nose along the gland on his wrist. He inhales what should have been the disgusting scent of another Alpha in a rut, but it was Deku so it was delectable. Made his skin tingle with arousal. It was spicy and bitter, but that’s exactly what Kacchan likes.


His teeth sink into the thin skin and Izuku’s painful cry only spurs him on, digging the canines in almost to the point of puncture. He knows to stop. He doesn’t want to hurt him. Not yet.


“You’re mine, Deku. Gonna eat you up…”


Katsuki grinds his ass down on Deku's cock, more as a tease because he knows he wants to fuck him. Deku is terrible at controlling his urges. He can feel him trying to grind his dick up into him, with no regards to lube or prep. At least Katsuki has enough wits about him to do that first.


“Whatcha want, Deku?” He teases, pinning scarred wrists to the bed below. He knows what he wants. Wants to fuck Katsuki like an animal. Dig his crooked fingers into his hips and bruise him. Claw him. Bite him. Mark him. But he wants him to say it out loud. Beg for it, like an Omega. “Wanna fuck me? Gotta say ‘please…’”


Mossy green eyes dark and hazy, Deku’s already so gone, he doesn't even bother to put up a fight. “Kacchan...I- I want… Let me fuck you, p-please…” he whines helplessly, breathless, already so desperate while he bucks his hips up into Katsuki.


Doesn't mean he's gonna get it.


Katsuki forcibly flips him over, face down onto the bed. Normally he'd be sweet on Deku. Kiss him across the scars and freckles on his back. Make him sigh and moan with warm sleepy pleasure. Maybe whisper some sweet shit into his ear. Deku likes that. Makes him feel special. But today is different. Today is not normal. Today they're beasts and the way he lubes up his fingers and slips two in easily, quickly setting a rough pace is the proof that there's nothing sweet about it at all.


Izuku claws at the sheets and keens, low and needy. He tries to grind his cock against the mattress while pushing his hips back against relentless fingers. It's messy and uncoordinated,  but it doesn't fucking matter. Not when Kacchan pulls out and digs his fingers into his hips, raising him off the bed onto elbows and knees to mount him. Presenting him like a mate. The slick head of his cock presses into his twitching hole and Katsuki growls as he sinks into his heat.


Deku’s tight around him. Always is, and his body is always hungry for more. He pulls him in until they’re pressed flush together. Normally he waits for Izuku to get accustomed to the stretch but instead, Katsuki quickly sets a brutal pace, hips slapping against his ass while trying to rid himself of the first serving of morning arousal. The first few days are the worst, they’ll probably fuck again right after. Maybe Katsuki would even let Deku top him.


But probably not.


Katsuki hauls his body up against his own, wrapping strong arms around his chest. His smaller, pliable body shifting with ease. He can't thrust as deep, but Deku’s pants and moans are worth it. He likes when Kacchan manhandles him, and he takes advantage of it every single time.


Calloused hands grip onto scarred biceps, holding Izuku in place to fuck into him hard and fast. The sudden wild stuttering of Deku’s hips makes it hard to keep the rhythm. “Deku, hold the fuck still!” Katsuki growls out, digging his fingers harder into thick muscled arms.


Crimson eyes travel the length of Izuku’s toned, scarred body below to find the source of his sudden behavior. “Holy shit, Deku...You popped your knot. You’re the one getting fucked...nothing’s even touching your dick and you popped it.” Katsuki teases, breathless and so turned on by Izuku’s lack of primal control. Voice deep and laced with ridicule as he watches Deku rock his hips. “That’s so nasty, Deku. You’re such a fucking slut.”


Izuku whimpers with humiliation. Tears stinging at the corner of his eyes. “No! No I-ah!” It wasn’t worth arguing over. He whines and cries out, eyes rolling back in desperation as his he humps at nothing on instinct alone, knot twitching almost painfully against the open air.



Katsuki chuckles darkly, “Oh yes you are, Deku. You’re so fucking desperate. So hot when you’re slutty...”


Deku doesn’t hear anything past that as Kacchan continues to spout words of degradation against his ear-


“You’re so filthy and desperate, Deku…”

“So fucking nasty...begging for my cock…”

“Can’t even control yourself, so slutty for me…”


His own mindless whimpers and the blood rushing to his head are enough to drown out any of his filthy drabble. The sting of rutting into nothing is too much and his dick aches. Begs to be touched, and Katsuki’s so nice to give him exactly what he wants.


A fist closes around his dick, tugs at his knot harshly and Deku cries out wantonly. It feels so good . So fucking amazing when the calloused palm runs across the underside of his cock, relieving some of the ache of primal arousal that left him dizzy and breathless. He fucks into it. Chases after the friction that he wants so bad. Wants to rut into his fist. Fuck into the tight grip. Come into something. Anything . The urge to mate ingrained in him was a fire that flicked and cracked in his gut and the only thing he could do was let it burn as he twitched in Katsuki’s hold.


“Fuck,’re such an animal. Can’t even help yourself from fucking into my hand. So nasty. Nasty for me...”


Izuku begins mewling, purring, whimpering in a not very Alpha way, and it drives Katsuki crazy. He’s coaxing, calling out to him. It’s what he imagines an Omega in heat sounds like when they’re eager to mate; not that he knows what that sounds like firsthand, but he’s not an idiot. He’s been curious. He’s seen porn in his early days of trying to figure out how to handle his urges. Deku’s cries ring in his ears and reverberate through him, filling him with a need to claim and mark him as his own.


Katsuki’s had his own cravings to mate before. He gets them everytime he has Deku trapped beneath him while in a rut. But this time, with Izuku so blissed out and lost to primal urges, it’s tenfold. Any coherent thought he had was gone as he pushes Izuku against the bed, face down into the pillow with a rough hand buried tight into his wild, tangled curls. He can feel his own knot swell inside of Izuku’s throbbing heat. Can feel the tightness around him and he grinds down with restricted movement.


Any shift he could muster sends chills up his spine. So good. So perfect it's almost painful how amazing Deku feels, especially when he begins rutting wildly into Kacchan’s tight fist again. His knot is heavy and swollen in his hand and Izuku’s struggle to buck into him feels like a fight or flight response that has Katsuki instinctively biting down hard against Izuku’s neck to soothe him like a struggling Omega. He immediately reacts to it, whimpering helplessly but completely stilling, besides the gentle rock of his hips into the grip around his cock, as if lost to Kacchan’s touch. His mind is hazy, eyes unfocused with fat tears falling down his cheeks while he mutters and whines into the pillows, “K-kaccha~ fffuuc- yesyesyes...”


Katsuki growls, harsh and deep, baring his teeth like a warning to others though there was no one else around. Possessive, but that’s definitely not what Kacchan would call it. His grinding is frantic as he searches desperately for release. The scent of fresh blood from the bite hit his nose as he trusts erratically, knot pulling at Deku’s rim until he was drooling and coming, filling him up with cum dripping down trembling thighs.


He rides out his orgasm and doesn’t even care to notice Izuku coming, crying, wailing and spilling onto the sheets below as Katsuki continues to painfully tug at his waning knot. Begging him to stop but still hoping he won’t as he claws wildly into the pillow from oversensitivity. Katsuki pulls out, dropping them both to the bed, both limp and tired with skin tingling. Warm and fuzzy. Brains feeling floaty and satisfied. Katsuki laps at the blood on Deku’s neck and purrs at the coppery taste on his tongue.


Temporarily satiated, Katsuki feels himself lulling back to sleep, exhaustion tugging at the back of his mind, but Deku’s bucking him off and is on him all too quickly for him to react. Strong arms pin him down as Izuku feels somehow larger than he actually is and looms over him with canines bared.


Growling in the back of his throat, Izuku licks at his own teeth this time while he snarls darkly, “My turn, Kacchan…”