10 Years Ago, childhood

Izuku and his friends... well Kacchan and Izumi's friends were parading through the forest with Izuku at the back. Kacchan was being lifted in the air by Izumi while he set off explosion like a floating sparkler. When they were crossing a log over the creek, Izumi lost her footing and focus, and she and the blonde both fell into the water. Their friends were concerned, but they just shrugged it off.

"You idiot, watch where you're going!" Kacchan playfully jabbed at Izumi. "It was your loud explosions that made me lose focus!" she fired back. Their playful banter was cut off when a hand reached out to help them. The hand came from the weakest member of their group. "Are you guys okay? I was worried you got hurt bad." The look in his eyes, the gesture, he was... 'Worried about us!? Like we're weaklings!? Like him!?' ...showing these ingrates kindness they didn't deserve. That was the first time Izuku Yagi had to learn how to block a hit.

Present

Izuku had revisited the same forest he and his childhood friends used to play together in. At first, it was a fun place with good memories. Later, it made him feel hollow, empty. Like he was never meant to be their, unwanted. Now, it slightly angers him, remembering the abuse he had to endure for no reason. Walking past the creek, he went deeper into the forest for a secluded place to learn about his quirk.

He picked up a stick and set it on fire. No smoke, no heat. He tosses the stick into a puddle, but it still burns. 'Flames that don't burn, but affect a person's mental state... like a mix of Dad and mo-... Inko's quirks. So, can I control the flames?' Izuku put down his notebook and raised his hand at the stick. The green flame rose up from the stick. Izuku moved it around, and clenched his fist to put it out. 'Pyrokinisis! I can reuse the fires I've lit, which makes the stamina drawback practically non-existent!'

Izuku practiced by creating large waves of flames, and directing them past the trees in a zigzag motion, circling around and coming back to him. As it turns out, he could also absorb the flames into his body to replenish his stamina. After doing this for a while, he began to feel a headache, the recoil of overusing the pyrokinisis. A cup of water cleared that up though. Izuku then lit his feet on fire and took off into the air. It was a bit wobbly, but he got the hang of flying quickly. His movements were smooth, he used his hands to direct himself. 'Even Izumi and Kacchan didn't get the hang of flying this quickly!'

Izuku's good mood came to a halt almost immediately. He stopped and just hovered in the air with dejected eyes. 'I mean... Yagi and Bakugo.' Izuku slowly descended to where he left his things. He had another move to try. Covering his fist in green flames, he punched a tree. He felt the impact, but his fist was barely fazed. He made the flames burn brighter, and struck the tree harder. He didn't even feel his fist connect, but the tree did. 'These fires are thick! Defensive properties.'

Izuku tried to experiment by placing his hand on his face. It was difficult to breathe, but he learned he was immune to the spine-chilling sensation he inflicts on others. The brighter these cold flames burn, the denser they are, but the faster his stamina drains. The flames he's left to burn can be sustained passively, but these incapacitating fires need more focus and energy. 'I could use this for capture moves! Man, cold flames are great! I wish I got it sooner. But then, I'd still be with them, and they're conditional love...' Izuku shook his head. 'They were never family to me. I don't need them holding me back anymore. I have to focus on getting stronger! I got an easy trial run, but if I get cocky I'll be as good as dead.'

Casting aside pointless thoughts, Izuku spent the day completely focused on his flames. Before he knew, sunset was on him. He put on his metal respirator to hide his lower face, a hoodie to hide his hair and flew off into the city. 'I'm still green. Nothing too big, maybe some alley guys.'

Musutafu

Izuku was patrolling the city from its rooftops to its streets, doing his best to either blend in or use his flashy quirk as little as possible. At around 10pm, he was considering calling it a night, until he heard a glass bottle breaking. He went to investigate and found two alley punks holding purses. Probably stolen.

"Not a bad haul, bro! We'll be eating good tonight!" One wearing a red beanie said. "You got that right! Burgers, booze, maybe some stripper ass to finish it off!" One wearing a dark green overcoat said. That was everything Izuku needed to hear. "Pardon me." he spoke up. The crooks looked to see a short hooded figure. "Am I correct in assuming that doesn't belong to you?" The two of them smirked. "Yeah, so what!? Go play hero somewhere else, brat!" Izuku slowly walked towards them. The beanie-wearing crook just shrugged. 'No one'll see us this deep in the alley!' He raised his and and shot orange flames. "So long, rug rat!" Izuku was consumed in a wave of flames.

"Poor kid. Dying like a hero. Pffft! Oh who am I kidding, he was nothing!" The overcoat thug said. As they were about to walk away, a voice caught their attention. "We're not done yet." They turned around to see the boy surrounded by a pillar of bright green flames, and the burglar's fire was against the walls. "Also, who said I'm a hero?" The Vigilante ignited flames on his back to shoot towards the two. They didn't have time to process it, it looked like a demon was coming for them. He uppercutted one off his feet, and kicked the other against the wall. They didn't fall as easily as the first one, but they were clearly shaken.

"Fuck you!" Another wave of flames was shot at Izuku, and tried to make a run for it. They weren't nearly as fast as they should've been. Izuku was unaffected physically by the flames, and took off to the sky, aiming to cut the robbers off before they could leave. As they made it to a nearby dumpster, a wall of hot flames stopped them. "Are these yours?" Izuku asked, hovering above them. He actually struck fear into their hearts. He pulled both his fists back to his sides, and flew down at the street thugs. The green devil flying toward them was burned into their minds and would haunt them for a long time. Izuku delivered two condensed fire punches that knocked the two out.

When he landed, he breathed heavily, surprising himself at what he did. 'I can control other flames, too! Even if they're from a person!? Holy woah! I couldn't control all of it, but it's something!' He tried putting out the fire, and as he did he felt something. The impulses of greed, apathy for others, love for sick thrills. Those were the feelings the thug's flames emitted. Izuku can detect a person's emotional state by the heat they emit. The hotter they are, the easier it is. His good mood was shut down when he realized what awful people lied in front of him. He made sure the bastards were tied up and was ready to use one of their phones to call the authorities. But something caught his eye. Beneath the dumpster.

He found a hatch. It led to a staircase that led to a small room filled with stolen goods. Izuku debated with himself, but remembered that he needed supplies to keep doing what he does. Not much, he just took food, water, a couple thousand yen and a first-aid kit. After a few minutes of looting, he called the authorities. With that done, he left the criminal's hideout exposed. Before he left, he took one more thing: the dark green overcoat on the other one's back. Izuku took off into the night, purposely leaving lingering green flames on the pavement like an artist leaving a signature of his work.

...

The cops arrived to where they tracked the cellphone. They found two unconscious thugs, and an underground hideout. "Oh my God, it's the Super Criminal Bros! We've been hunting them for a year now! Who could've done this?" one cop said as he dragged the two away. His partner looked at the familiar green flames on a surface that shouldn't be able to sustain fire. 'Our vigilante friend again.'

Meanwhile

Izuku was hopping over the rooftops, before landing on the ledge of a skyscraper, perched out of the sight of windows. 'I stole from criminals! Two wrongs don't make a right!' Izuku chastised himself as he looked at his stolen loot. His good nature told him that this was wrong, but his survival instincts said it was necessary. He has no one but himself. There's nobody around to help or look out for him, he knows that well already. Sighing, Izuku took out some takoyaki and ate. 'Heroes get payed for protecting people and throwing villains in jail. I guess this is my payment as a vigilante.'

After finishing his meal, Izuku looked at the green overcoat he took. It would have to be his blanket, and his big, yellow backpack his pillow. He was actually slightly looking forward to the next morning. There wouldn't be anyone to beat him up. Before dozing off, Izuku reached into his hoodie and pulled out two small pictures of his family. "Goodnight Dad, goodnight Grandma."

The Next Day

Izumi and Bakugo were walking home after a boring day of school. "Do you think something was missing today?" Izumi asked the spiky blonde. "Yeah, I didn't feel like I was asserting my dominance enough today." Katsuki said. They both scratched their heads in thought. "That's it! We didn't say hi to Deku!" Izumi realized. "Oh yeah. Come to think of it, when was the last time we saw the damn nerd? Fuck it, who cares. Tell him I said he's worthless scum." Bakugo bid farewell to his partner in crime. When Izumi got home, she went up to the attic.

Knock knock*
*Crash!*

She used her telekinesis to send the hatch flying off its hinges. 'Oops. When was the last time this place was looked after?' She flew up and saw the attic dusty from nobody cleaning it, and school books lying on the floor. "Jeez, Deku, when's the last time you cleaned up here?" Nobody was there to answer her. "Hey! I'm talking! Where the hell are you!?" She grew frustrated by the lack of response until she saw a note with All Might's signature on it. 'What's this?' Her eyes widened when she saw what was on the other side.

...

Inko and Toshinori returned home, the latter turning on the news about recent updates on a troubling topic. They found their daughter slouching on the couch with a shattered look about her. "Izumi, dear what's wrong?" Izumi didn't answer immediately. "...Mom, Dad, when was the last time you saw Izuku?" A strange question. But it took them a concerning amount of time to think about. Before they could answer, Izumi raised a slightly burnt piece of paper with All Might's signature.

I'm sorry, but I can't take anymore. I didn't ask to be born this way, and I didn't mean to be a burden. I want to know why you hate me so much, but I guess even that is too much to ask. Well, you don't have to worry. You won't have to deal with me, I won't be missed, and I won't burden anyone else. It's a win-win. Goodbye Yagi's.

Izuku "Deku"

The family was completely shattered by what they just read. Izumi confirmed it wasn't a suicide note since he left with his bag, but the truth is undeniable. Izuku ran away. They pushed him away.

Breaking News

"The green fire vigilante has struck again, capturing two criminals that have been on the wanted list for a year. The criminals awoke with a fright and refused to say anything about their attacker. All the police learned is that he is a brutal outlaw with no restraint, unlike our heroes. He is suspected to be armed and dangerous, wielding cold, green flames that don't go out for some time. First sighting of his strange quirk was in Musutafu near Aldera Middle School."

Their heart sank to the pits of their stomachs. Izuku was out there, alone and defenseless, and the vigilante was in the same area. Inko had flashbacks of her last husband dying, and broke down in tears. Izumi still looked like a broken soul. Toshinori's blood ran cold at the thought of his quirkless son having to fend for himself on the street like he had to. Little did they know, their assumptions were way off base.

Elsewhere

A shadowed figure sitting in a chair surrounded by medical machinery just finished watching the news. "My, my. This Vigilante has an interesting quirk. Igniting the flame of fear into others, and in just two nights, he's made the news. I'm impressed, child." He grinned widly, thinking of how useful the vigilante could be.