Chapter Text
Katsuki decided a long time ago, Izuku couldn't be a hero. Not only was he quirkless but he was also very sickly. Asthma, allergies, a heart condition. You name it and Deku probably had it.
The realization hit him back when they were still brats playing hero in the park. Izuku passed out from the heat one summer day. They had barely been playing for thirty minutes when the little nerd suddenly dropped to the ground, still as a corpse. It was the first time Katsuki truly understood just how weak his best friend really was.
To make matters worse, heroism seemed to run in Deku's veins like the blood his heart barely pumped through them. Even the slightest sign of trouble or inconvenience had the boy rushing to the aid of others, oftentimes at his own detriment.
A swirling out of worry and jealousy quickly consumed Katsuki. Unable to understand his own emotions he tormented the boy who had been raised alongside him like a brother for nearly a year before his mother finally found out.
She had been furious and for weeks the two fought over his treatment of the other until finally Katsuki broke and wailed in his mother's arms all his worries and fears.
After that outburst, Katsuki was taken to a talented child psychologist. It wasn't easy for him, having inherited his mother's fiery personality and pride but eventually he managed to work through both his insecurities and his fears regarding Izuku's mortality and health.
Izuku, the sweet, forgiving Izuku, was just happy to have his friend back.
After that the two of them became inseparable. Katsuki fought off izukus bullies and carried around an extra inhaler and EpiPen. They still fought over Izuku becoming a hero but overall they were closer than ever.
It was after a particularly bad asthma attack that Izuku finally gave up on being a hero.
Katsuki left to grab some drinks from the cafe during lunch break. Izuku overheard another student getting harassed in the hall and rushed to intervene without a second thought. His opponent had him pinned in seconds. Unaware of Izuku's condition the larger boy slammed him harshly into the wall effectively knocking the air from his lungs. The resulting attack sent the green haired boy to the hospital wheezing and gasping for air. Being roughed up, even only a little left his frail body bruised and broken.
That night when Katsuki visited Izuku, he finally gave up.
“You were right Kaachan” we wheezed through shaky breaths, tears already streaming down his cheeks “I'm too weak to be a hero. I'd just die the second I tried t-to help”
Katsuki held him close as he cried, hating everything in him that he had been right. It was bad enough that fate had denied his brother a quirk. Why did it have to give him such a sickly body as well. Maybe if he were healthy he could have had a chance.
Izuku was depressed for weeks after, until All For One was defeated.
All Might stood in front of the camera, moments after his battle with the world's strongest villain. We're there once stood a strong hulking hero was now a shriveled, elderly corpse of a man.
“If it hadn't been for the help of the other heroes and the quirk analysts I would have never succeeded today.”
All Might's retirement was announced shortly after the repairs began in the now leveled Yokohama. Despite the end of his favorite hero's career and the cataclysmic events of the last 48 hours Izuku found new purpose that day.
All Mights words kept ringing relentlessly in his mind and before he knew it he was researching how to become a quirk analyst. What made this even better was the fact that UA had the best hero support program in Japan. Not only did he have a new dream, he could also still go to school with Kaachan!
As expected Katsuki and Inko were fretful when he told them all of this. Ever the worry warts they tried to discourage him from pursuing anything even remotely heroic adjacent. In the end it was Katsuki's mother that convicted the two of them it would be ok
“It's just a desk job at the end of the day and he basically does that shit already. I mean you've seen his notes right?”
In the end Izuku applied to UA. While Katsuki was training and studying heroics for the hero entrance exam Izuku was pouring over his notes and studying every subject he could think of in preparation for his own exam. He cried with joy when the acceptance letter came in.
Now here he was on his first day of UA high walking up the steps with Katsuki at his side.
“You got your inhaler?” The taller huffed, hiding worry behind a gruff aditude.
“Yes Kaachan, and my Epi”
“What about your heart medicine. I don't need you passing out on your first day. It's be annoying as hell if I had to come save your during the entrance ceremony”
Izuku rolled his eyes at his brother's antics. Honestly it was like Kaachan thought he'd die if he just admitted to being worried about him.
“I took it this morning like always”
“Do you hav-”
“The forms excusing me from PE are in my backpack” another eyeroll. “I'll be fine Kaachan! I'm not THAT fragile.”
“Tch” the blonde scoffed but continued through the gate regardless and despite Izuku's protests walked his brother to his classroom in the Support program before heading towards his own homeroom.
“Listen up extras! Your looking at the next number one hero!” He'd become number one for sure. For himself and for Izuku!