Chapter Text
Chapter One: In the Beginning
They are constantly at each other’s throat.
At least, that’s what Izuku sees it as whenever Katsuki and he cross paths. There is no “hi” or friendly chatter anymore. Not like there was any to begin with but still, the moment their eyes lock, all hell break loose. No one tries to stop them when they start swinging- even their teacher Aizawa has gotten sick of getting in between them when they are suddenly all quirk and no play. He does demand they take their shitty rivalry out on the training field instead of demolishing their living quarters like a couple of barbarian animals. Even gives them an all access pass to Ground Beta so he doesn’t have to get a call every time they sneak out.
Already the couch and kitchen table had to be replaced. The scorch marks are still there because they’re harder to remove and there’s a sizable dent the size of a fist on the left wall besides the tv. Luckily the tv hasn’t suffered the same fate as the coffee table.
Sometimes they don’t make it to the training field at all and just duke it out outside the dorms where everyone can see just because they can’t hold back.
Izuku doesn’t remember when he starts fighting back this hard or engage in such savage battle with Kacchan; he distinctly remembers, when they were are ground beta that he wasn’t going to be Katsuki’s punching bag but he hasn’t expected it to turn out the way it has.
With his fist meeting tender flesh and feeling bones break from using his quirk. At this point, he doesn’t give a fuck what damage he causes as long as he can get the fiery blonde to back off.
And Katsuki takes it.
He takes the hits like a champ and fights back harder until he can’t bring air to his lungs quick enough and he’s panting from exhaustion on his back and clothes singed.
There’s always a smile on his face afterwards and Izuku wants to smack it right off of him. Who could be happy about getting their ass handed to him? Surely Katsuki isn’t that batshit crazy to enjoy Izuku one upping him in a fight. In fact, he expects anger mostly. Not that that happy, drunk off his ass laugh that follows every time the One for All user beats his ass to the ground.
It goes like this for weeks.
Like clockwork.
In class they’re fine but everyone can sense the tension bubbling beneath the surface-waiting with baited breath to see who will throw the first punch. If they suddenly threw caution to the wind and ended up trying to throw the other out the goddamn window. Neither one acknowledges the other when they’re being taught but the second the bell rings and they are free from the scrutinizing glares from their teachers, they’re at each other’s throat.
Slowly though, their fights turn into something more.
The first kiss happens on accident.
They are fighting in the courtyard and no one is around this time. Katsuki is coming at him, eyes gleaming with something unfamiliar but dangerous. He intends to cause as much bodily damage as he can with his next attack. And Izuku has stopped thinking. Because hell, he has done enough of that trying to figure out how things between him and Kacchan went to shit. Once the blonde is within reach, he grabs the hand that is coming towards him, activates his quirk to pull the blonde close before planting his lips against his without so much of a thought.
Izuku honestly expects to taste the sweetness of nitroglycerin but like Katsuki’s explosive, unpredictable personality, Izuku would be denied even that when they make out. It’s probably his own form of punishment for how Izuku treats him on the battlefield.
Everything in that moment screeches to a halt.
The green haired teen watches Katsuki through half lidded eyes as different emotions play across his face; shock, disbelief, anger so potent Izuku can taste it in his mouth. He expects the closed fist punch to the face and he doesn’t stop it. He falls on his back, Katsuki towering over him and breathing heavily.
The two quirk users stop fighting after that because the blonde runs off.
Later, Izuku claims he just wanted to get the upper hand on Katsuki during their fight for once and promises not to do it again.
Ha. Like he could keep that promise.
The second time though wasn’t an accident in the least.
He grabs the blonde when they were coming back from class, no one stopping to give them a second glance when he half pulled, half dragged the struggling teen with him. Their classmates had long since gotten used to them disappearing somewhere to beat the crap out of each other so it was no surprise when they took off. When Izuku finally finds a secluded spot-between two greenhouses no one ever visited that late in the day-he uses his quirk to push Katsuki against the wall and smother his lips with his mouth in a fierce kiss that takes Katsuki’s breath away.
To Izuku’s surprise, Katsuki doesn’t pull away and allows the smaller male to press between his legs, pushing him further into the wall.
Neither one questions what the hell is going on afterwards. Izuku apologizes anyways, says it’s an experiment even though he’s lying through his teeth, but Katsuki just glares half-heartedly and walks away.
Later, when Izuku is sure no one is awake, he sneaks to Katsuki’s room. He tells himself over and over as he makes his way to the others door that he wants to figure out if he’s going crazy because there is no way on god’s green earth did he want to make out with the blonde. When he knocks and the blonde answers, no words are exchanged because all Izuku can do is stare. He’s tugged inside by his shirt and the door slams shut before he’s shoved against the wood, doorknob digging painfully into his back. Red eyes are glowing despite the lack of light and it’s the only warning Izuku gets and he’s kissing him painfully; all teeth and tongue with no room to take control of the situation.
Katsuki tastes like ash and fire when he kisses his mouth.
A growl forms in the back of the smaller male’s throat when the blonde savagely bites into his lower lip and he pushes-hard. Katsuki staggers back from the force but before he can fall, Izuku catches him and practically throws him onto the bed using his strength alone. The other teen snarls, opens his mouth to tell Izuku to leave him the fuck alone but the All for One quirk user isn’t having it. There isn’t going to be fighting over this.
He feels the marks slither up his arms, green lightning sparking around him as his right-hand presses against Katski’s throat, cutting off his air supply.
It feels good, hearing the choked whine escape from parted lips.
Katsuki grabs at his wrists, palms sparking threateningly as he tries to pry Izuku’s fingers away. He only tightens his hold, fingers trembling and clenching tight as he marvels at the heavy pants that fill the air. Honest to God, he just wants to see how far he can push before he breaks his trachea and he ups his quirk to 14% and Katsuki gags.
Loudly.
Oh.
That’s a beautiful sound.
Izuku wants to hear more and before he can fully comprehend what he’s doing he’s grinding his hips against the others, feeling how painfully hard he is. And holy mother of God does it feel incredible.
Dark spots are beginning to form in Katsuki’s vision. His vision is fading. White noise floods his ears and fucking hell he is hard. He can feel his erection pressing against the confines of his pants and fuck fuck fuck does it feel good and Izuku must have noticed because no sooner does he feel the edge of orgasm the asshole pulls releases his neck and soon Katsuki is sucking in a lung full of air, gasping over and over as he draws it in and breathes out harshly.
Then he’s being choked again, harder. Feels when Izuku’s fingers dig deeper into his skin and he’s grinding down harder, panting in his ear as he gets off.
He releases a weak groan when it becomes to much and he cums in his pants.
Izuku gasps, his jerking erratically and Katsuki can’t breathe because the more Izuku thrusts against him the more to chase his own finish. His grip tightens to the point they both know he’s going to have problems swallowing in the morning. He only let’s go when he finds release himself, body stiffening above the taller teen before he lets go of Katsuki’s neck.
They don’t say a word to each other after it’s over. Not when Izuku goes to the kitchen to bring back two warm clothes soaked in water to clean themselves off with.
Not when Katsuki drops his pants without breaking eye contact and wipes away the cum from his abdomen.
Not when Izuku presses a soft kiss to his throat after they are clean.
He leaves without a word and Katsuki goes back to sleep.