Chapter Text
The scent of ozone and burnt sugar always lingered on Izuku’s skin after a heroics class. At UA, he was Midoriya, the bright-eyed kid with the blazing, emerald-tinted fire quirk. He was the boy who smelled like a campfire, whose knuckles smoldered when he was nervous, and who was currently sitting at the kitchen island of the the teachers dorms, trying very hard not to look exhausted.
"Problem child," Aizawa’s gravelly voice cut through the hum of the refrigerator.
Izuku blinked, looking up from his notebook. Shouta Aizawa stood there in his faded yellow sleeping bag, a mug of coffee in one hand. Behind him, Hizashi Yamada—Present Mic, though currently in soft sweats and a messy bun—was happily humming while stirring a pot of tea.
Since Aizawa had legally adopted Izuku a few months prior after a massive custody battle with his abusive father, Izuku had been thrust into a world of overwhelming warmth. Eraserhead and Present Mic were a package deal; they were husbands, they were his teachers, and now, they were his parents.
"You're burning through your glucose again," Aizawa muttered, sliding a plate of leftovers toward Izuku. "Your temperature is running high. Go eat, then go to bed."
"Thanks, Dad," Izuku mumbled, giving a tired smile. He dug into the food, letting the domestic warmth wash over him.
But beneath the smell of smoke and the safety of the dorms, Izuku could still feel the phantom sensation of cold water rushing through his veins.
---
Two hours later, the dorms were silent. Izuku slipped out of his window, dropping soundlessly into the shadows of the night.
He couldn't use fire out here. Fire left ashes. Fire left signatures. Fire was loud, bright, and uniquely ‘Midoriya’.
Instead, Izuku reached deep inside his chest, locking away the heat and pulling forward the cool, fluid current of his second quirk. He pulled a dark hood over his green curls and adjusted a sleek, pressurized mask over his face.
Tonight, he wasn't the fiery UA student. He was Flask.
Flask didn't just control water; he manipulated any liquid. In the grime of the Musutafu alleyways, that meant condensing the humidity in the air, redirecting puddles, or—in extreme cases—manipulating the sweat or blood of an attacker to throw off their balance.
"Drop the knife," Flask commanded, his voice muffled and distorted by his mask.
A low-tier thug whirled around, clutching a stolen purse. Before the criminal could even register the vigilante's presence, Flask flicked his wrist. The standing rainwater in the alleyway rose like a striking serpent, wrapping tightly around the man's wrists and ankles, pinning him to the brick wall.
"Damn it! Flask!" the thug yelled.
Izuku didn't answer. He retrieved the purse, tied the man securely with pressurized water cords that would hold for at least an hour, and turned to leave.
"Hold it right there, Flask."
Izuku froze. Walking out of the shadows at the end of the alley was Detective Tsukauchi Naomasa, his tan trench coat flapping slightly in the midnight breeze. Beside him, leaning against the brickwork with his capture weapon loosely draped around his neck, was Eraserhead.
Izuku’s heart slammed against his ribs. “Dad.” He thought.
"We just want to talk," Tsukauchi said, raising his hands peacefully. "You’ve been clearing out the underground rings in this district for months. We know you aren't malicious. If you answer my questions honestly, we can help you."
Flask kept his posture rigid, his mind racing. “The toll.” He thought.
Swapping quirks wasn't a seamless magic trick; it was a physical agony. Holding back his fire quirk meant his internal body temperature plunged dangerously low. His fingers were already changing colors beneath his gloves. If he stayed out here much longer, hypothermia would set in. If he went back to UA and used his fire, his blood would practically boil as his body rapidly adjusted to the heat. He was a walking thermometer of self-destruction.
"I don't need help, Detective," Flask said, his voice a gravelly, disguised pitch.
“True.” Tsukauchi’s mind registered.
Aizawa stepped forward, his red eyes flashing, his hair floating upward. "You're a kid. I can tell by your build. You should be in a classroom, not bleeding out in alleys. Let us help you before you get killed."
An ache bloomed in Izuku’s chest. Hearing his adoptive father use that exact 'Dad voice'—the one filled with fierce, hidden protection—while hunting ‘him’ was a psychological mind-bend that nearly broke him.
"I'm doing what the heroes can't reach," Flask said softly.
‘True.’
"And you think you're invincible?" Aizawa countered, stepping closer. "One slip up with that water quirk, and—"
"It's not just water," Flask interrupted, needing a distraction. He raised a hand, and the stale coffee left in a discarded paper cup nearby flew out, forming a swirling shield between him and the heroes. "I control liquids. And right now, I'm leaving."
Flask slammed his hands down. The rainwater on the pavement exploded upward in a massive, blinding fog screen.
"Eraser!" Tsukauchi coughed, shielding his eyes.
Aizawa lunged through the mist, his capture weapon slicing through the vapor, but Flask was already gone, scaling the fire escape with a burst of pressurized water at his heels.
---
At 3:00 AM, Izuku crawled back through his dorm window.
The moment his feet touched the carpet, the water quirk receded, and his fire quirk snapped back into place like a rubber band. The sudden, violent shift in temperature made him crash to his knees, gasping for air. His teeth chattered violently while steam literally began to pour from his skin.
“Cold, so cold—no, hot, burning—“
He clutched his stomach, dry-heaving into his trash can. The psychological whiplash was suffocating. At UA, he had to pretend he was a hot-headed, passionate fire-wielder. He had to laugh with Bakugo, train with Todoroki, and look Aizawa in the eye while lying through his teeth. In the streets, he was a silent, cold tide. He was fracturing himself into two completely different people, and the seams were starting to fray.
A soft knock on his bedroom door made him freeze.
"Izuku?"
It was Hizashi.
Izuku shoved his vigilante gear under his bed, threw on a baggy hoodie, and forced his body temperature to stabilize, though his hands were still trembling. He opened the door.
Hizashi was holding a mug of warm milk, his expression soft but deeply worried. "Hey, kiddo. Shouta just got back from a rough patrol, and he said he felt your room’s temperature spike from the hallway. You having nightmares?"
Izuku looked at Hizashi—the man who had spent the last three weekends helping him study for English finals, the man who made him pancakes every Sunday. The guilt tasted like ash.
"Yeah," Izuku lied, his voice cracking. "Just... a lot on my mind."
Hizashi stepped in, setting the mug down and pulling Izuku into a massive, warm hug. He smelled like vanilla and hairspray. "You're safe here, listener. You don't have to carry the weight of the world on your shoulders. Your dad and I have got your back, okay? Always."
Izuku buried his face in Hizashi's shoulder, a single tear slipping down his cheek. It evaporated into a tiny puff of steam before anyone could see it.
"I know," Izuku whispered. "Thank you."
He would keep running. He would keep saving the people in the dark that the light couldn't reach, and he would keep playing the golden student in the daytime. He would bear the burning heat and the freezing depth, because that was his burden to carry.
But as he hugged his foster father back, Izuku realized the hardest part wasn't evading the police or fighting villains. It was knowing that the people who loved him most were the ones he was running from.