So. I wanted to bring up a quirk theory I heard suggested once, and have THOROUGHLY researched. It comes up in a lot of my fics and I think it’s so important in explaining Katsuki. MENTIONED UA TRAITOR SPOILER DON’T READ IF YOU DON’T WANT TO KNOW!
Nitroglycerin is, in real life, prescribed as a medication. It relaxes blood vessels and can alter heart rate - usually slowing it down. This is a controlled, medicated prescription because in LARGE amounts… well…it’s slowing down the heart - that can be pretty freaking bad.
We know that Katsuki - at least in his hands - produces nitroglycerin. He gets this from his parents combined quirks - his father’s acid and his mother’s glycerin. I am not as certain of glycerin/glycerol effects, but one or two articles I sifted through did say that in SOME cases heart rate can be slowed down as well - others sped up.
Where I’m going with this is, typically, people born with quirks have some sort of natural defense against them. It’s why OFA causes such a strain on the user’s body, especially Izuku, and why Aoyama gets sick using his quirk - they weren’t theirs to begin with. Now, I know not EVERY quirk has built up defenses, and every quirk has a drawback (Aizawa’s dry eyes, Uraraka’s puking, Iida’s engine stall - etc etc). But, overall, I think most quirks come with a natural defense. There’s always been debate over whether or not Katsuki will or won’t lose his hearing - maybe already has since he’s so loud. I PERSONALLY think his body probably gave him sturdier ears to prevent that, but that’s just me. And I also think that Katsuki’s body came up with a way to defend against the possibility of Nitroglycerin poisoning - only it might be the biggest drawback of all.
Anxiety and Anger can MASSIVELY boost heart-rate.
Who is angry all the time? Katsuki AND Mitsuki.
Is it possible that Katsuki’s anger/anxiety issues stem from his body trying to keep his heart rate up? Is it possible that the nitroglycerin and glycerin require their bodies to combat slower heart rates? (Maybe for Mitsuki her heart is doing the opposite of slowing and just constantly going fast - keeping her in a mental state that’s higher?)
We all know that, while, sure, Katsuki was always a bit of a shit - he and Izuku WERE friends before he got his quirk. We put so much of the blame on his personality - on the ego he got from his quirk being epic. And I don’t dispute that as being part of it. But is it possible his quirk genuinely screwed with his brain chemistry?
Is it possible that his tendency to ‘explode’ partially gets worse when his body is trying to dispel large amounts? That his anger and anxiety decrease after he explodes shit, not just because he let something out emotionally…but physically? Possible that he is calmer after because his heart rate can slow but not dangerously so because he isn’t full of nitroglycerin?
I doubt that a doctor or anyone would ever look into this as a possibility because there would probably be an assumption that it was all ‘bad attitude’ or ‘personality’ maybe even simple upbringing - what with Mitsuki’s anger issues and all.
But think about how angry Katsuki gets - some of the pivotal moments in his and Izuku’s lives. If my theory is correct, he already would have a baseline of high anger and I truly think anxiety. Just because his body is trying to keep his heart steady. (the more the nitroglycerin pulls it down, the higher his anger/anxiety would work to pull it up). But add on an external moment of anxiety or anger? It’s going to be for all LITERAL intents and purposes like a ticking time bomb.
Katsuki falls in the river? He’s scared? His anxiety is going to be even higher. Someone comes to help him? BOOM.
He gets extreme anxiety while the sludge villain is suffocating him? Rabid ‘monster’ BOOM. Izuku saves him? He’s vulnerable/anxious and now even more angry? BIGGER BOOM.
He gets muzzled after an anger episode? Triggering his anxiety over suffocation? RABID BEAST ONCE MORE MID PANIC ATTACK.
He thinks he’s responsible for the fall of the greatest superhero? That the world is falling apart and it’s his fault? Yeah…that normal anxiety? Now skyrocketing. His heart rate is going crazy, his nitroglycerin builds up - both sides are attacking one another and he needs to boom the hell out of someone he knows can take it - Izuku. Baboom!
Wakes up in a hospital where he hasn’t been able to dispel any nitroglycerin? Learns Izuku is still unconscious? (the love of his life) BOOM!
Katsuki’s body chemistry is literally ALWAYS fighting against itself. So when he starts to realize he’s an ASSHOLE and wants to change…. He is fighting an uphill battle in a nitroglycerin hurricane because his body is pushing him down in this war against its own chemistry.
And that, Ladies, Gents and Those of you in between, is why his character progression is that much more meaningful. Because he still begins to overcome himself - even with all of that happening. And THAT is why I love him.
