“Um, Kacchan? You can probably put him down now, I think he's unconscious?”
Katsuki's only response is a deep, growling snarl as his hand twitches around the throat of the villain they had been chasing. The villain is definitely unconscious, blood dripping from his nose and the corner of his mouth in dark rivulets. His face is a swollen mess, with bruises blackening the skin around his eyes, but Katsuki doesn't release his grip.
Izuku presses a soothing hand to Katsuki's shaking shoulder, dropping his scent around him like a well-worn coat in an attempt to soothe the Alpha’s sudden, irrational anger.
It is, arguably, the wrong thing to do.
Katsuki drops the villain and whirls around, crowding Izuku until he's pressed against the alley wall with his feet dangling- holding Izuku up with only one thick thigh wedged between his own. It puts him at the perfect height for Katsuki to jam his nose against his neck, inhaling deeply. It also puts him at the perfect height to feel the massive bulge tenting Katsuki’s pants, and Izuku fights to drag in air through the broken cartilage of his own bloody nose.
He keeps his voice steady and calm, keeps the panic from souring his scent, as Katsuki continues to nose at his scent gland. He lays his hand along Katsuki's jaw so that he can pull his face up to meet his gaze and the Alpha pro hero growls a warning.
“I need you to calm down, Kacchan,” he says soothingly, rubbing his wrist over Katsuki’s cheek. The scent catches his attention, pulls his face up so that he can rub his nose there and his crimson eyes close with a content rumble. With his other hand, Izuku activates the headset built into his mask.
“Deku? Everything good?”
It’s Kirishima on the end of the line and Izuku heaves a sigh of relief, grateful that he's the Pro on desk duty this shift. Anyone else and this situation could have been so much more awkward.
“Kirishima, I need you to check what Quirk this villain has. And I also need you to… I need you to, ah-” he cuts off with a ragged moan when Katsuki mouths at the pulse point on his wrist, fighting back the urge to buck against the Alpha’s knee.
“I'm fine! We're fine!” He swats at Katsuki's face, and then slaps him hard enough to jerk his head to the side when the Alpha growls at him again. “No, Kacchan! Bad boy!”
There's a snort in his ear followed by Kirishima's deep chuckle. “Did you just call Bakugou a bad boy?”
“U-um, yeah, ha. So, here's the thing-” he shoves Katsuki's head away when he dives back in, giving him a snarl of his own when he attempts to latch down on his wrist. Katsuki tosses him a look so wounded that Izuku almost presents right there, in the filthy alley with an unconscious villain only a few feet away. “I need you to call Kacchan's ERC. I think this villain has a quirk that jump started his rut.”
“Oh, shit,” he can hear the clacking of the keyboard, as Kirishima pulls up Katsuki's contact information. Katsuki bites down hard on Izuku's wrist, sharp teeth tearing through his skin and ripping another moan from his lips. Izuku powers up One-For-All and slams Katsuki to the ground, pinning him there with his arms crossed helplessly over his chest. It should make the blonde angry-rut or not, no Alpha likes being pinned- but Katsuki releases a soft whimper, arching his back as his hips rock upwards.
“An-any luck, Kirishima?” Izuku cradles his wrist close enough that he can see the bite wound, see the source of the heat that's radiating through his arm. There's a bit of blood trickling from the wound and Katsuki sniffs hard, trying to reach the source of the smell.
“You should probably come back to headquarters,” Kirishima says, his voice strangled, and Izuku's heart drops.
“What's wrong? No, Kacchan, stop!”
“Well, um. Deku, bro. You're listed as his emergency rut contact.”
Katsuki bucks his hips again and- surprised and stunned by both the news and the physical contact- Izuku punches him solidly in the face, his Quirk-boosted punch knocking him out instantly.
“Okay, I can see that I'm listed as his rut contact but I don't understand why,” Izuku's voice is thin, reedy with a plethora of emotions- the majority of which he is not ready to name- and his arms flail wildly in Kirishima's direction.
The red head crosses his arms over his chest and meets his gaze, steady and unwavering, while he waits for Izuku to calm down. Kirishima and Izuku had placed Katsuki in a secure room to ride out his rut but that was hours ago. Izuku is anxious over the whole situation and Kirishima isn't helping.
“Bakugou helped me fill out my paperwork, I find it hard to believe that he’d fill his own out wrong, dude.”
“But why me?”
There are so many things tangled in those three words and Kirishima just shakes his head, to Izuku’s dismay. Izuku deflates, slumping forward to rest his head against the Alpha’s chest.
Kirishima pats his head and says, “I know you don’t see it but Bakubro trusts you. You’re one of the only people that he finds worthy of his respect and trust. And besides, you two have been dancing around each other for years. So, why wouldn’t he trust you with this?”
“He should have told me. And he had to have known it was coming up, it's marked on his calendar,” he mutters into Kirishima’s chest, pounding his hand half-heartedly against his muscles. “It would be nice to be aware of this responsibility before the fact!”
“You know how much he's been working lately, you're the one who's been partnering with him on those extra patrols. And like you’re so good at communicating,” Kirishima snorts, still patting his head. “You’ve had a crush on him since way before Yuuei.”
“That’s why I can’t do this! I can’t just help him through this rut and then walk away! I… I l-lo-”
“I know. Help him through this rut and then talk to him,” Kirishima urges and Izuku sighs into his chest. “He needs you. Especially since this rut is boosted by a Quirk. It's going to be really hard on him.”
And Kirishima is right.
Ruts are hard for Alphas to endure without the assistance of an Omega: knots need a chemical found in Omegan slick to deflate, and the compound is not only hard to replicate in synthetic form but it varies from Omega to Omega. What works for one Alpha might not work for another. It's why so many Alphas take rut suppressants until they find a mate, even though they run the risk of damaging their own bodies. And with the headway made in heat research- focused on Omegas due to the often brutal pain of their heats- the majority of Omegas can manage their heats on their own. Science has yet to see such results in rut research. After being on rut suppressants for over a decade with yearly scheduled ruts, and with this rut influenced by a villain's Quirk, Kacchan must be in agony.
So of course, Izuku isn't going to let him suffer this alone. Not when Kacchan trusts him to help.
Izuku pushes the heavy door open, peering cautiously into the agency room designated for ruts and heats. His breath catches in his throat, damming his airway with the overwhelming scent of Katsuki's rut. He chokes on the cloying aroma, feels desire curl in the pit of his stomach, slick trickles down his thigh in response to the smell that is so purely Kacchan. The smell is sinful enough but the noises? And the image of Kacchan??
The Alpha is sprawled over the surface of the bed, feet jammed down into the mattress so that he can thrust his hips up into his fist. His blonde hair is plastered to his face, the dark makeup of his mask now just a smear over his cheekbones and the arch of his nose. There's cum spattered up his abdomen, and his thighs quiver with the strain of a rut that's gone on too long.
He's so strung out on his own pheromones and the agonizing intensity of this rut that he doesn't even look up to acknowledge Izuku, he just whines out a pitifully hoarse, “Deku?”
“It’s okay. I'm here now, Kacchan,” he's moving before he gives his feet permission, all the way to the bedside before he realizes it, and takes a quick detour to the mini fridge stored by the bed. He strips down to his boxers and grabs a water bottle before sinking beside Katsuki, and his hazy red eyes finally blink up at him.
“Deku,” he whines, relief dripping from the sound, though his hand never stops moving furiously over his blood-swollen length. Izuku slips his arm beneath Katsuki's shoulder to tug him into a half-sitting position, propping him up against his own chest.
“Drink some of this water and I'll help you feel better, Kacchan,” Izuku keeps his voice low, lets it rumble over the Alpha. He growls but Izuku bites down on the meat of his shoulder, hard enough to cow him into submission. Katsuki opens his mouth, throat working hard to swallow the cold liquid, hand still jerking hard.
He lays his hand over Katsuki's- slowing his frantic pace, to a languid glide- and the Alpha growls again, bucking up into their twined fingers. “I'm here to help you. There's no need to growl and snap at me, Kacchan.”
“Need… I need-”
“I know, Kacchan, I know,” Izuku whispers, reaching up with his free hand to card through Katsuki's drenched blonde strands. “We're going to get you through this and then we're going to have a long, long talk about communication and feelings.”
Katsuki shudders, drowning in Izuku's heavenly scent. He tosses his head to the side- baring his neck submissively for Izuku to sink his teeth into- and at the sharp penetration, he comes: gushes of warm fluid that coat their fingers, dripping lewdly upon the Alpha's stomach. The Omega laps at the blood trickling from the wound just above his scent gland and Katsuki lets out a petulant whine.
“I know, I know. It’s not where you wanted me to bite but that’s for later, after we’ve talked,” Izuku presses kiss after soothing kiss along the rigid line of his shoulder, strokes gently through his limp hair, waits patiently for him to come down from his orgasm.
“It's not enough,” Katsuki sobs, still achingly hard beneath their joined hands, slamming one fist angrily into the mattress as he shakes in Izuku's embrace. “It hurts, why does it hurt so much?”
“Do… do you want to try rubbing m-my slick on your knot, or do you want to f-fuck me?”
Katsuki moans at his stammered words, hand twitching under Izuku's but there are no words, just harsh pants as he tilts his head further to the side. Izuku presses his mouth against his scent gland, not biting down, just enough pressure to make the Alpha whine.
“Kacchan, I need to know what you want,” Izuku’s voice is raspy: his desperate attempt to hold back his own desires clear in the cracked sound. He’s quickly losing that tentative hold.
“You, just want you,” Katsuki turns abruptly, slides one leg over Izuku's lap- hitting his own burgeoning erection in the process, causing him to cry out- and he grinds down, rocking his cock against Izuku's. “I’ve always wanted you-”
“We are definitely talking about this when you’re coherent,” Izuku mutters, fingers clamping down hard on Katsuki’s thighs. “Just so you know, this is not how I planned on confessing. If I ever got up the nerves to confe-” Katsuki cuts him off, pressing their lips together. It’s messy, sloppy, savage: the Alpha’s teeth catch on his lower lip, splitting the plump skin and glazing their tongues in the metallic tang of his blood, causing Izuku to cry out. Katsuki hums his approval at the taste, pulling back just far enough for Izuku to see how his eyes are completely blown out, the crimson seeping into the whites of his eyes.
“Want to fuck you, want to sink as deep inside you as I can go, want to feel you tight around my dick,” Katsuki snarls, lips twisting with the words, and his fingers clench in the fabric of Izuku’s boxers. “Want to mark you, show everyone that you’re mine-” he drags his lips along Izuku's scent gland, inhaling deeply when arousal floods the Omega's scent. “Want to drench you in my scent. Want you. Only you can make it stop-” he breathes against Izuku's lips, fingers ripping into the barrier separating him from Izuku's warmth.
Izuku quivers at the words, heat coiling in the pit of his stomach and spreading outwards, threatening to overtake him. He fights the urge to submit- because one of them has to stay sane through this and Katsuki is gone. For once, his mind doesn’t clash with his Omegan instincts- the desperate need to make sure that Kacchan is okay coincides perfectly with the instinctual urge to please him.
“I’ll take the pain away, I’ll make it better,” he pants into Katsuki’s mouth. His boxers tear away with a jerk of Katsuki’s hands, leaving him covered only by the Alpha's body.
Katsuki shifts, slinks just far enough down the length of Izuku's body that he can slot his dick between Izuku's thighs. He rocks forward with a low growl, fingers sinking into his hips to yank Izuku towards him. His dick slides through the slick that drips from Izuku in copious amounts- dragging moans from them both- but his legs are trembling from exhaustion.
One thrust, two, three- and his cock finally catches on Izuku's twitching rim, punching the breath from Izuku’s lungs as he sinks deep inside him. His hands scrabble wildly, fluttering first along his shoulders then down the slope of his spine to clutch at his ass. Katsuki dips his head, curling his forearms beneath Izuku’s upper back as he presses his nose into the Omega’s scent gland.
“Kacchan,” Izuku moans, eyes squeezed tight as he buries his face in Katsuki’s hair. He shifts his knees, hooks his ankles against the backs of Katsuki’s thighs to spread his legs and pull him closer, until there is no space left between them. Pressed chest to sweat-slicked chest, they cling to each other as the heady scent of Katsuki’s rut drags Izuku into a pheromone-driven madness.
When he rolls his hips up, slamming against Katsuki’s cock, the Alpha shakes and tightens his arms around Izuku. His body thrusts mindlessly, seeking the overwhelming warmth of Izuku’s tight heat as the Omega croons broken praises into his ear. Katsuki is incapable of coherent words: he’s reduced to the rut-craze that drags guttural groans from him, that pulls his hips forward in jerky snaps. His tight grip paints finger-shaped bruises along Izuku’s shoulders, his teeth leave a trail of purpling indentations over his neck. His breath is a series of gasping pants, fiery on Izuku’s skin as his palms spark and sear little burns into his back.
it’s still everything Izuku has ever wanted, and somehow more.
Katsuki’s knot begins to swell, his cock throbbing as he slides one arm down to better angle Izuku’s hips- body running on pure instinct, brain cells drowned by the pungent aroma of Izuku’s arousal- so that he can hit Izuku’s prostate on the next hard thrust. Katsuki’s knot catches on his rim when the Alpha pulls back to shove back in: Izuku’s head thrashes as he keens, his nails sinking sharply into Katsuki’s skin. His brain is fried, he’s lost to the sensation of Katsuki as the Alpha takes what he needs from him, what Izuku freely gives.
All of his responsible ideals are thrown out the window when Katsuki sinks his teeth into the sensitive flesh of his scent gland, yanking his orgasm from him with a suddenness that leaves him screaming and clenching down impossibly tighter on Katsuki’s length. His knot tugs painfully on Izuku’s entrance and he shoves it in again, as Izuku’s eyes glaze over with pheromone-boosted pleasure. The Alpha latches down fiercely, fingers twisting into his curly hair to hold his head still, and his knot slips past his rim one last time to lock firmly in place as he comes hard.
Izuku jerks his head loose, just far enough that he can blindly search out the patch of neck where Katsuki’s own scent gland lies, and he bites down hard enough for his teeth to break the skin. Somewhere, deep down in the rational part of his brain that's buried beneath layers of lust, he feels the bond snap violently into place, settle into his veins like lightning zinging around.
Katsuki howls around the skin clenched between his teeth, hips still jerking as he empties himself within Izuku’s quivering heat- spurt after spurt of cum coating the Omega’s insides as he cooes and gasps for air. Izuku's eyes are blown wide, unseeing as he slides his arms up to wrap around Katsuki’s shoulders with his legs still spasming where they’re hooked around the Alpha’s waist.
The Alpha’s world fades to nothing- nothing except Izuku’s scent, anchoring him.
When he wakes, it's to gentle fingers massaging his deflated knot. He’s too exhausted to react but so is his cock- finally spent from hours of Quirk-boosted rut and his frantic attempts to bring himself to release. When the fingers leave, just for a second, he whimpers and they return immediately, coated with the musky scent of Izuku’s slick. He rubs the thick fluid into the skin at the base of his dick, an extra measure to prevent the fury of his rut from roaring back to life.
“How is Kacchan feeling?”
His Alpha purrs at the satisfied tinge to Izuku’s words and he lets the sound escape, too tired to fight it.
“Kacchaaaaan, I need words,” Izuku settles down beside him on the bed and Katsuki curls into the soothing warmth that he radiates. “We need to talk but I need to know how you're feeling.”
“Tired. Sore. Wanna sleep,” he mumbles into Izuku's side, eyelids heavy as he melts into Izuku's lap. His body is still trembling with exhaustion. “Can talk later.”
“We mated,” Izuku says, bluntly stating the obvious. As if Katsuki can't feel the bond humming in the back of his mind.
Katsuki can't even gather the energy to panic at that, though he feels the nervous fear thrumming beneath his skin.
Izuku senses it, fingers dropping to pet through his matted hair. “I'm not mad at you, Kacchan. I mean, I was. You should have told me that you put me as your rut contact. Like, before you did it,” Katsuki curls around him, body trembling as he hides his face. “Just so that I could have prepared, I would have said yes. I could never tell you no, I wouldn't want to. But you were in rut, and I'm not on birth control. I don't know how long we were tied. I need to know where you want to go from here.”
Katsuki mumbles into his skin, the sound so muffled Izuku can't understand what he says.
“Kacchan, I can't hear you,” he lowers his head, pressing his cheek to Katsuki's hair and the Alpha lifts his head a little to stare into Izuku's eyes when he repeats himself.
“Want you to stay my mate. Want you to have my pups. I'm tired of waiting to find the perfect time to ask you but I want you to stay with me. Be mine.”
Izuku's fingers clench in his hair, tears welling in his eyes as he smiles down at him. His heart pounds wildly, throwing his scent out in pungent waves. The Alpha purrs as he basks in the aroma of the Omega's happiness.
“Silly Kacchan, I've always been yours.”
Their post-rut checkup confirms what Izuku had theorized: Izuku is carrying Katsuki's pup.
Izuku bursts into tears, flooding the room with a scent so violently ecstatic that even the doctor tears up. Katsuki crouches to bury his face into Izuku's stomach, pressing kiss after kiss into his stomach while the Omega squeezes his arms around his shoulders.
“Mine, you're mine, thank you,” the Alpha babbles nonsensically, and Izuku runs his hand soothingly through Katsuki's hair.
“We're going to be parents,” Izuku says in awe, words soft and stunned despite already knowing before taking the test.
“The best parents,” Katsuki adds.
“It's not a competition,” Izuku laughs, rubbing his cheek in the soft strands of pale blonde hair.
“We're going to outparent the shit out of everyone else,” he says, “you hear that, kid? Your parents are going to raise the shit out of you.”
The doctor looks vaguely horrified but Izuku giggles and agrees.
“Kacchan, it's okay,” Izuku shifts the cooing bundle in his arms, motioning the anxious blonde to his side. He wipes his sweaty palms down the front of his pants and sinks gingerly beside the green-haired man. “You won't hurt him.”
With shaking hands, he reaches out and Izuku carefully hands their son over. He cradles him gently, staring down completely awestruck as he curls his tiny hand around one of Katsuki's fingers. Izuku leans forward to drop a soft kiss over the unusually thick blonde curls, smoothing down the tangled strands.
“He has your freckles,” Katsuki whispers, kissing along the smattering of freckles and huffing a quiet laugh when his nose crinkles up at the sensation. His mouth opens in a tiny yawn, fingers twitching against his own.
“He has your eyes,” Izuku smiles proudly, sliding until he can rest his head on Katsuki's shoulder. His raises his arm so that they're both holding their son.
“Your curls, my color,” the Alpha adds, and his voice cracks. Izuku wisely ignores the tears streaming from those red eyes. “Thank you,” he chokes out and Izuku twists to kiss along Katsuki's jaw.
“Thank you,” Izuku says, and he doesn't need to say anything else- Katsuki understands- but he adds, “I love you.”
Katsuki doesn’t answer but Izuku understands. There are no need for words when the Alpha turns to press their lips together, their son breathing softly in their arms.