Disclaimer: I don't own My Hero Academia. Or whatever else is copyrighted. This fanfiction is mine, though.
"Please stop! He's only five!" His mom is on her knees, and close to tears. Her hands are stretched out, trying to grab Shouto, but his father keeps him out of reach. When his father uses his fire quirk, she flinches and shrinks away. He grabs Shouto's wrist and squeezes it hard enough to hurt.
"He's already five! Don't get in my way!" And then he's dragged away, away from mom and getting closer to some room and he has a feeling that he's going to throw up again.
The training doesn't stop. It happens every morning and evening, ending only after he is satisfied. His mom starts pulling away, starts becoming more and more distant, and Shouto wonders what he would be like if she wasn't there, and only his father was. After she gets put in a hospital ward and he gets a more striking appearance, he doesn't have to wonder about that. She never comes back to the house.
A few years later, Endeavor is defeated. Well, not actually defeated. A villain with a water manipulation quirk manages to get the jump on the number two hero, creating a tsunami big enough to douse his flames and make enough steam to blind him, causing countless casualties to bystanders unlucky enough to be caught in the crossfire. Buildings were flooded, civilians were drowning, and some steamed alive. The villain takes an entire town hostage at one point, threatening to summon an even bigger tsunami. Shouto only sees that because All Might's name appears in the news. The number one hero had stepped in and with a well placed punch, manages to blow the water out into the opposite direction, as well as all the steam, and captured the villain.
Endeavor comes home angrier than usual. Calling the training brutal would be a huge understatement. He feels cold, yet melting at the same time and everywhere hurts. His father's angry yells of "How are you supposed to surpass All Might at this rate!" and "You can't become number one if you're this weak" makes his ears ring and his head pound. If there even ever was a time he cared about surpassing the symbol of peace, it definitely wasn't now.
He can't run out of here even if he wanted to, his father's too quick for that and any energy he had was gone dozens of exercises ago. He's lost count. It hurts to breathe and his vision's graying at the edges and blurring even though he's still looking at the fire made from Endeavor's quirk. He eventually loses consciousness though, and when he wakes up, it's three in the morning, and he's still in a puddle of his own sweat, blood, melted ice, and god knows what on the ground. As expected, Endeavor's gone. But what's unexpected was the set of fluffy towels and water bottle put in front of him.
He towels off, even though he's far from being clean, drags himself out of the room, drinks all of the water bottle, drags himself to bed and sleeps it off. He doesn't think too much about the water bottle, despite it never happening before.
It happens a few more times. He writes it off as his father wanting him to stay alive.
His father is irritated again, and he probably shouldn't push it, but one offhanded comment led to one comeback that might have dug too deep, and then one thing lead to another and all the emotions from the last few years bubble out and seep into every word he spits out. The yelling match is so loud, Shouto's honestly surprised the neighbors haven't filed a noise complaint before he's dragged by the arm into the training room. The yelling match didn't stop though.
The last thing Shouto recalls is swearing he won't ever use his fire side so he won't be like Mr. Number Two over there, and realizes he pushed it. He blacks out from the resulting "training", stubbornly keeping his fire quirk unused and going down faster than normal.
And when he wakes up, he sees a blurry, unfocused blob of bright green and a cup of water floating in the air. His eyes snap open and his world focuses, but the green floating blob thing doesn't. It moves about, setting the water down near his arms before floating towards the door. Shouto stares at the water like it was part of the green floating thing, even though he knows it most likely wasn't. After a few moments, he decides it's just water and is about to drink it when the green blob thing appears. It is translucent, and takes a vaguely humanoid shape. No matter how much he strains his eyes towards it, all the features and details are vague. It was about as visible as the words on a soaked piece of paper.
Then he realizes he's been staring at it for a while now. It lingers in the doorway, holding a blanket on its side, starting to fade and become more solid, as if it can't decide and is just switching between the two. It's in the middle of fading and becoming more transparent when Shouto spoke.
"What kind of quirk is it?" His voice is hoarse from disuse and kind of quiet, but it's clearly heard in the silent room.
The thing becomes more solid and eventually, he can make out a boy with green hair and what looked like freckles on his cheeks. It's still not quite opaque, not quite real-looking, but it's enough to see what it is. When it walks (hovers?) closer to where he is, he becomes more wary and sits up, ignoring the bruises and burns. It opens its mouth, and makes an clear attempt at talking, moving its lips to form words, but no sound comes out. It tries again, moving its lips and half a word comes out. It looks shocked, and elated, before starting over.
"My name is Midoriya Izuku." His voice is high pitched, young, and loud enough that Shouto freezes. Not literally, but his muscles tense and ache and his eyes go towards the doorway. The corridor remains silent, with no stomps indicating his father heard. He then looks at the thing, no, Midoriya, and raises a shaking hand towards what looks like Midoriya's legs. His body is numb from overuse, but he can't have some villain attempt to kidnap the number two hero's son. Ice crystals start forming, and dart towards Midoriya's feet. He gets up from the ground, ice quirk activated, and is about to advance on the intruder before Midoriya's legs phase through the ice supposedly shackling him to the ground.
"Wha-" "I'm not here to hurt you I swear! I'm not even alive I promise!" The... ghost? blurts out. Shouto's jaw stays open, not finishing his word. His ice quirk deactivates, and after a beat of silence, with Midoriya looking like he wanted to sink into the ground and Shouto trying to process what exactly was going on, Shouto's jaw snaps shut.
"Please explain."