Chapter Text
Katsuki Bakugo and Izuku Midoriya were born on the same street, one day apart, under the same sky that always seemed to smell faintly of smoke and asphalt.
They shared toys before they shared words. They ran together, fell together, bled together. And when the first signs of quirks began to bloom among their friends, they watched together too — waiting for the day their own powers would awaken.
It was Katsuki who went first.
One bright morning, after a scuffle with some older kids, a small spark had danced in his palms. The smell of burnt sugar filled the air — nitroglycerin. The world gasped in awe. Katsuki grinned, his palms steaming. “Explosion,” he declared, with the confidence of a god learning the word for thunder.
Izuku had clapped for him, eyes wide, heart full.
Not with envy — not yet — but with hope.
And then, days later, when Izuku’s turn came, the same smell filled the air again.
Not from Katsuki’s hands… but from every inch of Izuku’s skin.
Doctors would later call it a mutation-type variant. Where Katsuki’s sweat glands had evolved in his palms, Izuku’s entire body had changed. Every pore produced the same nitroglycerin-like substance, the same faintly sweet, volatile scent. But no matter how hard he tried, it refused to ignite.
He could sweat. He could shimmer under the light like liquid glass. But not explode.
For all intents and purposes, he was a bomb without a fuse.
“Try again!” Katsuki shouted one afternoon, hands on his hips as Izuku stood shirtless under the sun, sweat glistening on his trembling arms. “Come on, nerd, you have to be able to blow up something. Anything!”
“I’m trying!” Izuku gasped, clenching his fists. “It’s not— it’s not lighting!”
He stomped his foot, frustration building with the heat. Drops of sweat hit the dirt — hissed faintly — but nothing more. Katsuki flicked a spark from his hand and it popped like a firecracker, dust scattering around them.
“See? Like that! You’ve got the same stuff, right? You just need to—”
“I know! I just— it doesn’t listen to me!”
Katsuki’s grin faltered for a second, and for the first time, he saw it — that fragile crack in Izuku’s voice. The kind that trembles between anger and shame. Between wanting to prove yourself and wanting to disappear.
The explosion he wanted wasn’t in his quirk. It was in his chest.
At school, the difference grew sharper.
“Bakugo’s the boom boy!” the other kids said. “Midoriya just sweats like a scared dog.”
Izuku smiled through it, because Katsuki would always snap at them first — “Shut up! He’s stronger than any of you losers!” — but sometimes, he saw the way Kacchan looked at him when the day ended and the laughter faded. Like he wanted Izuku to catch up. Like he was waiting for him to stop being fragile.
Because Katsuki didn’t want to leave him behind.
And Izuku didn’t want to be left behind.
That night, Izuku tried again in secret.
He filled his bathtub halfway, sat in it, and stared at the thin film of sweat rising from his arms and shoulders. It shimmered on the surface like oil. He whispered to it. Begged it.
“Please. Just once. Let me be like him.”
His reflection didn’t answer. Only the faint ticking of cooling pipes and the hum of the house around him.
He brought a lighter to the surface — just a test, just a spark.
A sharp pop, a flash — and pain.
Water splashed up as he yelped, falling back, a red welt blooming across his arm. The flame had caught, but only for a breath. Just enough to hurt him.
He sat there, clutching his arm, breathing hard. Tears mixed with sweat, and everything stung.
And still, he whispered, “Just once…”
Later, when Katsuki found out — when he saw the bandages and the red skin — he didn’t shout.
He just sat beside Izuku on the curb outside their homes, knees pulled to their chests, the streetlights painting them gold. For a long time, neither spoke.
Finally, Katsuki said quietly, “You don’t have to explode to be strong, you know.”
Izuku turned to him, eyes wide, not used to that tone.
Katsuki didn’t look back. “I’ll blow stuff up. You… you figure out how not to.”
And somehow, that made sense.
Two halves of the same spark.
That night, as they walked home together under a sky full of stars and distant city lights, Izuku felt the same warmth in his chest he’d always felt since they were little — the one that burned, even without fire.
He didn’t know yet that someday, that warmth would ignite the world.