Experiment One: Heat Resistance Is A Superpower

Midoriya Izuku is a very warm person.

Not his personality (though that's also true). It's his quirk. His quirk is that he's warm.

Izuku has had his quirk since he was born, burning his way into the world at a hearty temperature of "barely feverish", and it's never dropped since. According to Books, which Izuku reads a lot of, this means his quirk is Morphic; he is quite literally made of warm.

His dad was Morphic too; his insides could catch on fire and there was so much of it he could even breath it out. There isn't a lot of use for a quirk like that, but it looked pretty awesome. According to the doctors, Izuku has received his father's quirk. He loves it.

When Izuku is four, he gets to go to daycare, where he impresses everyone with it. Morphic and Shape quirks are impressive to small children. There's a Shape kid with a big tail, and everyone wants to be his best friend, which proves the rule.

Izuku, on the other hand, decides he wants to be Bakugou Katsuki's friend. He's loud and pushy and probably has an Energy quirk. Something like fire. When Izuku pushes to be his friend, Bakugou Katsuki says once Izuku finally figures out how to set himself on fire, Izuku can be his sidekick.

To Izuku, this is a wonderful idea, a dream come true. The first thing he had ever grown attached to was a news broadcast where a hulking blond man walked straight out of a comic book to rescue a seemingly infinite amount of people, laughing all the while. Izuku could watch that video for hours. In fact, he does watch it for hours. Daily. He wants to be a hero like All Might more than anything.

Izuku thinks that it's wonderful All Might has the power to save so many people and bring hope to everybody. Katsuki thinks it's awesome that All Might strong and everyone loves him. They are four years old, and to four-year-olds, nuance is fake.

But they both watch the newscasts of this saviour of the new age of superheroes, and Katsuki is a magnetic kind of person who makes friends instantaneously, and he looked at Izuku and said "you can do this with me".

The heat didn't prickle at his cheeks, and his skin didn't flush, because he doesn't know what it means to heat up, and he doesn't even know what cold is. But if he could, he'd have blushed with pure joy.

He wants to be a hero.

Kacchan's quirk accelerates, and his behaviour along with it.

Izuku's quirk and personality, on the other hand, are at a standstill.

He's never gotten any warmer, and he's never gotten any braver, but Kacchan's boisterous attitude has jumped from "bossy" to "outright violent".

His quirk is explosions. They scatter from his fingertips, sparking off the sweat on his hands. Reactive quirks are impressive; Izuku knows this because the teachers won't stop telling Kacchan how impressive they are, and how wonderful it is that he's gotten one.

At first, Izuku is ecstatic, and heat rolls off him like sun-warmed pavement; he's a perfect sidekick. He's practically a recharge station.

But, as stated before, Kacchan's behaviour accelerates.

A lot.

It starts with "You can read it like Deku, that means useless!", marring him with an obscure and unpleasant nickname forever.

And Izuku ends it somewhere around Kacchan shoving a kid to the ground and marching forth, hands sparking ominously.

Izuku is five and a half and he's watched at least fourteen recordings of All Might standing up to bad guys and Kacchan isn't a bad guy, is he? But he still stands up, puts up his fists, and tries not to cry.

Kacchan's heat can't touch him, but he and his friends have fists, which are just as good.

Izuku spends a lot of time being angry.

Not…angry, angry, like Kacchan is, but so frustrated that the warm air rises in great billowing puffs that make his blanket float off him. He simmers. Clenches his teeth. Complains a lot. He is five years old, and there's nothing five-year-olds love more than whining incessantly.

"He's not heroic," Izuku insists over dinner for the eighth time, "he beats up kids which is villain stuff."

"I'll talk to his parents, sweetheart," says his mom.

Izuku doesn't think that's enough.

Well, it technically is; Kacchan doesn't attack people after that. But he doesn't stop being mean. He still includes Izuku and seems to want him there, but Izuku spends a lot of time being angry all the same.

Most of the time, they go hang out at empty lots where Kacchan can use Izuku's warmth to gather up his sweat. He says that the more you work on it, the stronger the quirk is going to get. Izuku ("Deku") is fine the way he is, Kacchan claims, since the muggy ring of heat radiating off his skin is pretty much perfect for gathering sweat, but it'd be way cooler if he could light his skin on fire at some point.

Maybe like green fire, he continues, because the dull, dead-leaf pallour of his hair would look 'stupid and ugly' with normal fire.

Izuku scowls at the gravel, takes a drink of water and breathes out steam. That happens sometimes. His insides are hotter than his outsides, like his dad, and he…

It is at this point, Izuku, age six, suddenly realizes that he can't actually turn his quirk off.

He's gotten into heroes as an industry by now. He's been paying special attention to people with quirks that work like his do, like Endeavor, who has the same quirk as his dad, except on his outsides, and it looks like it's always on.

When he gets home Izuku meticulously records notes and compares them and then starts looking up as many Morphics as possible until he stops dead at the obvious conclusion:

There is no existing hero who has a Morphic quirk that's just kind of there.

He doesn't know what else to do from there, so he stares at his notes for an hour until his mom calls him for lunch and then he never mentions it to another living soul.

This is the story of an eight-year-old.

Initially, I mean.

Izuku, age eight, loves experiments.

His quirk is weird and no one really thinks it's weird? But the thing is, weird quirks, you can do weird things with them. Heroes are good at that. And anyway, heat is the most common kind of Quirk ever and everyone has a bajillion ways of using it so Izuku is enterprising by wanting to do weird quirk stuff.

He gets an All Might lunchbox for his birthday, left to the side when he and his mom go out to celebrate, and it's not until the next morning that he actually moves to put it on the shelf with all his other All Might collectables. But his fingers trace along the indents in the metal and his brain hits the phrase 'melting point' so fast Izuku can't remember the thoughts that brought him there.

And Izuku, who loves experiments, decides he likes the thought anyway. He collects his notebook and his pencil and his eraser.

Now all he needs is a blowtorch.

He'd ask Kacchan but Kacchan will never let him test how hot his explosions get, and he'd ask someone else with a heat Quirk but everyone else's heat quirks are different and Izuku isn't supposed to talk to strangers.

He also isn't allowed to take people's blowtorches without permission, but he's, uh, borrowing it. Like, he's not taking it off the property. He just wants to turn it on and put it on his skin and see what happens.

According to The Internet, the air-only torch he finds at his third construction site scan will heat up to around 1,900 °C, which is a good start. He'll find an oxygen-fed torch later if he doesn't set himself on fire. He'll also do it if he does set himself on fire, because the scientific process just works like that. He doesn't make the rules.

Izuku is very very small, and very very quick; you have to be when you have a friend like Kacchan. He ducks in and out of the shed-like building clutching his prize, hides behind some tarps, and fidgets with it until he can get it to turn on.

Izuku doesn't feel heat like normal people. He doesn't feel the…vibrations? Vibrating molecules? Friction? When molecules go really fast they make friction and that's how burns happen. That doesn't happen to Izuku. People who can make energy have this thing called single progression molecules, which is the same thing hero costumes are made of! They grow fire-making Quirk Skin in a lab to make them, and Izuku was obsessed with this fact for a few months. There are multiple people growing multiple types of Quirk Skin in multiple labs! Kacchan tells him to shut up and stop being gross whenever he brings it up but Izuku can't help it.

Well anyway, it's important, actually. He found out passive Morphics don't exist. You have to intentionally morph into stuff. That's the point.Endeavor's face isn't constantly on fire, it's just his hero thing.

Which means Izuku isn't just a Morphic. His existence produces energy. A…Izuku scrambles to stitch all the terms he's read in Books together. R…Reactive Energy quirk? Or something. The point is, he's made out of a material that manipulates heat. And that means he can…he can…erm…

Well, Izuku hadn't gotten past that in his research, but he's sure he'll figure it out by the time he's ten, because he's an experimenter, and he's got a blowtorch right here to help him on his way.

After it runs long enough, Izuku wiggles his fingers in front of the tip of the flame, and then sinks it deeper until he can turn his hand all over in the fire. The heat feels like its curling around his fingers; Izuku thinks he's always warm because there's a shield of temperature stuff that might wrap around him naturally, on account of him being made of weird new skin.

It's not like Weird New Skin is weird, or new. Which is kind of a bummer. Reactive Form is the fancy science term for "people who have skin made out of weird things". It's just that they're not normally energy or fire things. They're usually textures and stuff, or twisting light around.

Izuku's never heard of someone with heat-related skin. He hopes they can grow it in a lab.

The fire starts seeping through his Warm, and for the first time in his eight years of life, he experiences hot. It sinks into him more than an hour of his hand on a stove iron could ever achieve. His molecules don't do friction, so it mostly just sort of tingles and goes numb. He can actually see his skin vibrating. It's so cool.

After a few minutes of this, his skin is starting to glow red, and the texture starts feeling…weird. Too numb. Izuku stretches out his palm, and to his awe, the skin breaks and parts into molten slag, with bright glowing yellow lines being pulled open like scars.

He blows on it like you'd blow on a fire, and it erupts into sparks and flickering flame.

He can catch on fire.

He's going to need to figure out a better way to pull it off, though. He'll get back to that!

Using one hand and his thighs to carefully turn the blowtorch off, holding his molten hand up high, Izuku tries to make as many notes about his new condition as he can:

- Not gooey or liquid like actual lava. Kind of stretchy. Melty rubber, maybe.

- Hand works fine.

(Would Kacchan be mad if he saw?)

- Prickles a bit. The parts where he blew on it to make a fire feels extra tingly.

- Vibrating so hard that it's shaking all the way down his arm. Feels like a massage chair, or a chihuahua.

- Not sure how to get it to cool down.

Izuku stares wide-eyed at his raised arm, actually thinking about the situation for the first time since he decided he needed a blowtorch.

It…it will cool down…

…Right?