Chapter Text
The morning sun usually brought a sense of fresh beginnings, but for Izuku Midoriya, it mostly just brought humidity. And humidity meant his hair wasn't the only thing puffing up.
Sitting at his kitchen table, a small, dense cloud the size of a soccer ball hovered just above his messy green curls, occasionally crackling with a tiny, harmless spark of static electricity. Izuku stared blankly at his breakfast, propping his chin up with one hand while using his quirk to mindlessly condense a miniature fog barrier around his orange juice.
Izuku took a long sip from his glass, immediately feeling the slight tightness in his throat ease up. That was the primary drawback of his quirk, Cumulus. He couldn't create moisture out of thin air; he had to utilize the water vapor in the atmosphere or, more often than not, the water reserves in his own body. If he overused it, he didn't just get tired—the extreme dehydration caused his hair to lose its pigment.
Right above his left temple, a distinct, thumb-sized tuft of hair had turned completely, starkly white during a particularly intense training week the previous year. It hadn't changed back.
The front door to the Midoriya apartment had swung open without a knock. Katsuki Bakugo walked straight into the kitchen, tossing his school bag onto a chair and snatching a piece of toast right off Izuku’s plate.
Katsuki was, by all societal standards, a ticking time bomb of a teenager. He possessed a terrifyingly powerful Explosion quirk, a temper to match, and a vocabulary that consisted largely of threats. But to Izuku, he was just Kacchan—the loud guy who lived next door and lacked basic boundary awareness.
"Good morning to you too, Kacchan. Splendid to see you're still practicing your breaking-and-entering skills," Izuku said, not even looking up as he smoothly redirected his floating cloud to block Katsuki from grabbing a second piece of toast. The blonde’s hand plunged into the vapor, losing its grip. "And please, refrain from eating my breakfast. Some of us actually need the caloric intake, whereas you seem to operate entirely on spite and nitroglycerin."
"Shut up! I don't need a lecture from a walking weather report," Katsuki snapped, though there was no real venom in it. He sparked a tiny explosion from his palm, instantly dissipating a chunk of Izuku's cloud. "Get your shoes on, or I’m leaving you behind."
---
The dynamic between them had been established over a decade of shared history. When they were four, everyone assumed Katsuki would become the undisputed leader of the neighborhood. His Explosion quirk was flashy, destructive, and immediately obvious.
Izuku’s quirk had manifested a few weeks later. He had sneezed, and a perfectly spherical storm cloud had enveloped his entire head, raining directly into his eyes.
The neighborhood kids had laughed, but Katsuki hadn't. Even at four years old, Katsuki had watched Izuku blink away the rain, look up with a terrifyingly calm expression, and mentally condense the cloud into a tiny, solid marble of pressurized vapor that he then flicked directly into a bully's forehead.
They weren't rivals. They were a team. Katsuki provided the overwhelming offensive pressure, and Izuku provided the tactical, chaotic battlefield control.
But middle school at Aldera Junior High was an exercise in pure boredom for both of them.
The teachers were uninspired, the curriculum was redundant, and the students were far too obsessed with who had the coolest quirk. Izuku spent most of his classes staring out the window, casually manipulating the condensation on the glass into intricate geometric patterns while keeping a notebook open on his desk.
To the untrained eye, the notebook was full of chaotic scribbles. To anyone with a degree in heroics or tactical analysis, it was a terrifying breakdown of human psychology and mechanical physics.
"Midoriya!" the teacher called out, slamming a hand on the chalkboard. "Since you find the clouds outside so fascinating, perhaps you can tell us the primary drawback of a kinetic-release quirk when operating in an enclosed space?"
Izuku blinked, his expression shifting into a mask of pure, unbothered apathy. "Assuming the user doesn't possess a secondary dampening factor, the primary drawback is atmospheric overpressure leading to acoustic trauma and internal hemorrhaging for both the user and bystanders, sir. Or, in layman's terms: you blow yourself up because you didn't check the ceiling height. Can I go back to ignoring you now?"
A few students snickered. The teacher’s vein popped, but he couldn't exactly argue with the accuracy.
Beside him, Katsuki snorted, leaning back in his chair. "Stupid extra," he muttered under his breath, though his eyes lingered on the corner of Izuku's desk where a tiny, dark storm cloud was spinning like a top.
When the bell finally rang to signal the end of the day, the teacher handed out career aspiration forms, scoffing lightly as he looked at the top two papers.
"Well, I’d normally ask you all to seriously consider your futures, but it seems Midoriya and Bakugo are both aiming for the U.A. High Hero Course," the teacher announced, causing a collective murmur to ripple through the remaining students.
"Obviously," Katsuki barked, kicking his legs up onto his desk. "I’m going to be the number one hero. I’m going to surpass All Might, and everyone else here is just a stepping stone."
"And I'm just going along to make sure he doesn't accidentally commit a public relations atrocity within his first week," Izuku chimed in, packing his pens into his bag. "Someone has to hold the leash, and unfortunately, I'm the only one immune to his minor explosions."
"Who are you calling a dog, Deku?!"
"The one barking at a perfectly innocent desk, Kacchan."
As they walked home through the bustling streets of Musutafu, the contrast between them was stark. Katsuki walked with an aggressive, wide-stanced stride, hands shoved deep into his pockets, looking like he wanted to fight the concrete. Izuku strolled beside him, a permanent, lazy smirk on his face, a thin mist swirling around his ankles to keep his shoes clean from the street dust.
"You're looking pale today," Katsuki noted suddenly, glancing at Izuku’s hair. The white tuft near his temple seemed just a fraction of a millimeter wider than it had been that morning. "Did you skip your water intake during lunch, you idiot?"
"My hydration matrix is currently at eighty-two percent, which is perfectly acceptable for normal ambulation," Izuku replied smoothly, though his throat did feel a bit dry. "But thank you for tracking my biological functions, Kacchan. It’s not creepy at all."
"Keep talking and I'll blast that smirk right off your face."
"You've been trying for ten years, Kacchan. Your success rate is currently sitting at an abysmal zero percent."
Before Katsuki could ignite his palms, a sudden, wet sloshing sound echoed from the dark underpass they were about to walk through. The air instantly grew heavy with the stench of sewage and industrial chemicals.
From the drainage grate, a massive, towering mass of olive-green sludge surged upward, two glowing, manic eyes forming in the center of the liquid chaos.
"A cloak of skin... yes, you'll do perfectly!" the Sludge Villain roared, lunging directly toward Katsuki.
"What the hell—?!" Katsuki reacted instantly, throwing a massive right hook fueled by a blinding explosion. The blast rocked the underpass, but the flames simply dissipated against the fluid body of the villain. The sludge wrapped around Katsuki’s wrists, pinning his arms and beginning to suffocate his mouth.
Izuku didn't panic. His mind, usually a chaotic mess of witty comebacks, instantly shifted gears into high-speed calculation.
‘Liquid-based composition. Viscosity implies high water retention mixed with organic waste. Physical impacts are useless due to fluid dynamics, but the eyes and teeth are solid anchor points. Katsuki's explosions are creating a vacuum, depleting the oxygen inside the mass, which is accelerating the suffocation process. Need to disrupt the surface tension and separate the mass from the host.’
Izuku’s eyes sharpened. The lazy, sarcastic teenager vanished, replaced by something clinical and terrifyingly focused.
"Kacchan, cease thermal output immediately. You're accelerating the asphyxiation matrix," Izuku commanded, his voice dropping into a rapid, monotone mumble as he took a sharp, deep breath.
He thrust his hands forward. A massive, incredibly dense wall of freezing, localized cumulus vapor erupted from his palms, driving straight into the center of the Sludge Villain like a solid battering ram. The cloud wasn't soft; it was packed so tightly with moisture that it acted like a high-pressure water wall, wedging itself between Katsuki’s torso and the villain's main mass.
To pull off a cloud of this density, Izuku had to draw heavily from his internal reserves. He could feel the sudden, jarring wave of fatigue hitting his system, his skin growing pale as the moisture was rapidly wicked away to fuel the quirk. Deep within his green curls, another tiny strand of hair faded from vibrant green to a stark, snowy white.
"What is this?! Smoke?!" the villain yelled, struggling as the dense cloud began to rapidly absorb the moisture from his fluid body, drying out the outer layer of his sludge into a crusty, immobile shell.
"Not smoke. Condensation with a highly concentrated electrostatic charge," Izuku mumbled under his breath, his fingers twitching as his vision blurred slightly from the sudden onset of dehydration.
‘Voltage calculation: approximately 50,000 volts required to disrupt nervous system transmission without causing permanent cardiac arrest to the primary host.’
"Clear," Izuku muttered.
Snap.
A violent, blinding flash of blue lightning cracked through the dense cloud, surging directly into the Sludge Villain's eyes. The villain shrieked, his grip instantly failing as his liquid body lost all cohesion, splattering across the concrete walls of the underpass in a stunned, unmoving mess.
Katsuki fell to his knees, coughing violently, gasping for air.
Izuku exhaled a long plume of gray steam from his mouth, stumbling slightly as his knees buckled from the drawback. He immediately pulled a high-electrolyte sports drink from his side pocket and downed it in three massive gulps, the color slowly returning to his face.
The sharp, analytical look in his eyes instantly dissolved, replaced once again by his trademark half-lidded, amused expression. He walked over and offered a hand to his childhood friend.
"Well," Izuku said, his voice returning to its usual drawl, though it was a bit raspy. "That was certainly an adventurous way to avoid doing our homework. I give the performance a four out of ten. Great villain aesthetic, terrible execution."
"Shut... up..." Katsuki wheezed, batting Izuku's hand away and pushing himself up, wiping the remaining sludge from his face. He glared at the scattered pieces of the villain, then looked at Izuku. His eyes flicked to the side of Izuku's head, noticing the fresh white hairs blending into the green. "You used too much juice, dumbass."
"A minor calculation error based on atmospheric humidity," Izuku replied, adjusting his backpack and running a hand through his hair, completely unbothered by the new white streaks. "Come on. If we're late for dinner, your mom will make us eat the healthy dynamic-nutrient soup again, and frankly, I'd rather face another sludge monster."