People think that Bakugou Katsuki is angry all the time, that he's just furious at the world—a barely contained bomb of rage waiting to explode, just like his quirk. It's not exactly true, but it's a useful lie, so he doesn't ever correct anyone.
See, Katsuki loves his quirk. It's violent and explosive and, most importantly, powerful. It's a quirk that will make bad guys one day tremble before him, just like they do before All Might.
What he doesn't tell anyone, can't ever tell anyone, is that it also hurts. When he was little, it was the sting of a snapping rubber band—annoying, but quickly forgotten. But his quirk grows and matures as he does, as he learns to use it, make it more—and the pain grows with it.
He can't burn himself with his explosions—his skin is adapted to take it on the outside. But under his skin? Where the sweat that ignites gathers? It's tender and aches all the time like a first-degree burn. It throbs and aches, and the slightest touch can make him suck in a breath.
Weirdly, it doesn't hurt to use his quirk… it's the times between. The longer he goes, the worse the ache, the pain. Using his quirk more, developing it more, seems to have increased how much of the explosive compound in his sweat is held under his skin, and it… it burns from the inside.
No matter how much it hurts though, Katsuki loves his quirk. He loves the moment he first ignites an explosion, loves watching it grow, loves seeing the reds and golds in his flames that are only seen in fire, loves the unique scent his explosions give off gasoline and ash. He loves using the force of his explosions to fly. Loves the feel of air rushing around him from the force of his blasts. He loves being the eye of a hurricane of smoke and flame and sparks. When he's using his quirk, adrenaline takes over and he forgets that he was ever in pain, forgets about everything but how fiercely alive he feels.
He loves his quirk. He's going to change the whole fucking world with his quirk. He's going to make Endeavor look like a hack with his so-called "hellfire." He would not change it or give it up for anything.
No matter how much it hurts.
And, yeah, there are days it hurts a lot, and he has to hide it. There's no way to fix it—he's looked. Any painkiller you can get over the counter was useless by the time he was ten, and anything strong enough to help isn't something he can safely use long-term, so, he just… sucks it up. It's just pain and it doesn't actually do any damage or it would have been fixed at some point when he'd been in Recovery Girl's care.
It's surprisingly easy to hide how much pain he's in all the time. Being in constant pain makes people irritable, grumpy, and prone to angry outbursts. The thing is, Katsuki's always been kind of a hothead, forgive the pun. He comes from a family of hotheads—you don't have to look any farther than his mother to see where he gets his temper from.
So he got more irritable and his temper got worse as he got older—and watching his best friend develop a superquirk out of fucking nowhere doesn't help matters. No one thinks anything of it though. Everyone he ever meets quickly learns that Katsuki doesn't merely have a short fuse, he pretty much has no fuse. Like his explosions, from nothing to BAM pretty much zero-point-zero flat.
There are days when it's so bad, he goes off just to get some relief, let out the storm that gathers under his skin like a ticking bomb. Those are the same days where the littlest things, the tiniest annoyances make his temper flare supernova bright. The same days where he yells at the top of his lungs at anyone in earshot. There's a petty part of him that takes satisfaction in watching others rush to get out of his way when he's in a mood like that, but mostly, it's just a relief not to have to deal with anyone when he's hurting that badly.
When his head is clearer, he knows that his temper isn't doesn't exactly make him a good role model. It doesn't make him an ideal hero, like All Might, who's not only stronger than anyone, but he's kinder than anyone too. Katsuki cares—he wants to be a hero to help people, not just because he wants the glory, no matter what people think. He doesn't think those goals are mutually exclusive, but he can—objectively—see why someone like Deku could be a more steady and reassuring presence than he is.
He's not going to let Deku beat him. The universe started with an explosion; it may be arrogant but Katsuki feels like he touches that beginning with every explosion he unleashes. He's going to tap into the Big Bang that lives under his skin and be the greatest hero there is.
If the price is a little pain, well, he can live with that.
AN: Katsuki is the kind of character I really want to love, but that temper makes me want to throttle him, and I wondered "what could this kid possibly have to be so angry about all the time?" Then I remembered watching a loved one struggle through chronic pain and how much that changed them. So sprung the idea "what if he's not angry all the time—what if he's in pain all the time?" Thus—this short. Hope you enjoyed. If so, please leave kudos/comments.
Title inspired by Nikita Gill's "The Cosmic Storm Inside" (which seems to kind of describe Katsuki to me).
"Your body was designed
to contain a cosmic storm.
It is no wonder that sometimes
your head and heart hurt so much
that you may just explode.
It takes a nebula,
a cosmic storm of epic proportions
falling apart to create a star."