" What'chya doing? " chirrped through his head.
"Making a bomb," Katsuki grunted.
Izuku, who was diligently grinding sea shells in a mortar and pestle they'd borrowed from his mom, echoed the grunt. Sweat beaded across his forehead.
Katsuki had his own hands wrists deep in a bowl of charcoal he was mashing up by hand. He had put on some leather gloves to do so, just in case it wasn't magic that blew up in his hands but his sweat.
They worked outside a cave a half-hour hike away from the tribe's canyon home. Katsuki had known the cave existed for a year now, but it wasn't until he had a dream last night that he remembered the now fading memories of his long-ago science classes.
The dragon, who couldn't even remember his full name from his past life, looked at both of the boys in audible confusion, then at the bowl of yellow liquid some feet away.
" Is that…pee? "
"Nitric acid," Katsuki said. "From bat guano."
" Eww, come on man, that's messed up, how are you suppose to make bombs out of that? And why do you even have to make it if you can just use your magic? "
"My magic is something only I can use," he pulled out his arms and shook his hands, leaving puffs of black dust to rain towards the ground. "This way, anyone can do it."
"Even me," chirrped Izuku.
The dragon tilted its head, then narrowed its eyes.
" Why does this sound like a bad idea? "
"Because we're blowing up shit." Katsuki stood up and peeled off his gloves. "You done, nerd?"
"Yeah!"
"Got the yellow chalk stuff from your hometown, lizard?"
Ejiro reached behind him to pull a lidded-basket from between his wings. Katsuki had been particularly proud of that piece of work, because it meant Ejiro could fetch things from far away that he couldn't carry with his mouth since he wasn't yet big enough for Katsuki to ride.
"Sweet, now, I don't know the exact ratio, but that's where trial and error come in."
Despite having been grinding seashells all morning, Izuku had the energy to bounce in excitement, even giving a little cheer.
Ejiro, however, just gave a dragony frown-which was all in the ears and wings.
" You seriously had me fly all the way home for something to blow yourself up with? "
"Shut up, we're only doing small amounts and from a distance."
" How are you going to test it from a distance? "
That did give Katsuki pause. But only for a moment.
"You can do that spit fire thing, yeah?"
Ejiro did not look reassured. Even though he was a fire dragon, the most Ejiro could do was make a thin stream of fire that was mostly flaming spit. When he went moping around about his lack of prowess, Katsuki had him practice his aim till he could snipe down pigeons.
"Come on, it'll be sick." Katsuki gave his best grin, which Izuku mirrored with a fanatic like gleam.
Ejiro sighed. " Where do you want me?"
Katsuki had picked out a ridge of rock they could hide behind to observe just for the occasion, right above the bat cave. He very carefully (see, Ejiro? Careful.) mixed his first sample of charcoal, ground sea shell, and sulfer, then added a drop of nitric acid. Goose bumps prickled along his skin when it didn't immediately explode. It wasn't more than a spoonful.
"Alright," he said. "Take one."
He dumped the little black spoonful onto the flat stone twenty or so feet away from their observation point than dashed back cackling madly. Izuku chortled with him, doing some weird wiggle thing with his eyebrows. They both looked at the dragon expectantly.
With one last final sigh, Ejiro pulled his shoulders back and hacked up a thin stream of fire through his front fangs.
It splashed onto the little black pile.
…and sizzled out.
Izuku pouted.
"Welp, it was the first try," said Katsuki. "Let me go mix up take two. What do you think it needs more of?"
Eleven-year-old Izuku pinched his chin in thought. "Well, the sulfur and seashells are the least flammable thing I can think of, and charcoal's already been burnt, but I don't know much about the acid. You said acid breaks down components, yeah? Can make them into something else?"
"Yeah?" No, scratch that, Katsuki was the one with the know-how here. "Yeah." There we go, that sounded more sure. "Takes extra oxygen molecules out." Or was it hydrogen? Damn it. He should have written these down when he could still remember…as a baby.
Izuku, however, nodded, probably remembering more of Katsuki's slap-dash, reincarnated-blurred science lesson and said, "More of the acid, then."
Take two sizzled for a bit longer, but no go. The third, fourth, and fifth takes didn't do much either.
It was starting to get dark and a lot of the excitement had worn off when they finally got a hit that sparked, crackled, and smoked.
"Yes!" crowed Katsuki as Izuku yipped. "We're so close, I can smell it!"
" Smells like fireworks," Ejiro mumbled, who had long gotten bored and would have taken a nap if he hadn't been hounded on to be a lighter.
In his excitement, Katsuki made the next sample a little larger than the last. He wanted to be able to see what was happening this time.
"Okay," he said once he'd set it out on the blackened testing ground. "Go."
" Aren't you going to duck down? " asked Ejiro.
"I gotta see."
The dragon just sighed for the dozenth time that day and spat out a spark, much less enthusiastic than the first half-dozen ribbons of flame.
The world exploded.