Rewind
Chapter I: Rebirth
It was an accident, really, something one would expect from someone who had no idea what her quirk was or how to control it. All Eri knew was that Deku was hurt, and she wanted to help him, just as he was helping her. I don't want Deku hurt was the only thought in her mind. Such a pure, selfless thought, combined with her quirk and the imagination of a child resulted in something ... impossible when he caught her. An enormous flash of light came from the horn on Eri's head, and suddenly everything was different.
Ten Years Ago
"Eri!" Izuku cried out as he woke up ... only to realize he was much smaller than he had been before catching Eri. He looked around, utterly confused, only to realise that everything looked different, even though he had somehow ended up in his bedroom at home. Even the All Might merchandise was different, and less in number, and all of it was no less than ten years old. Izuku ran to where he kept his Hero Analysis journals to check the latest one, only to find a grand total of three journals ... and none had any of the local pros that had tried dealing with the sludge villain. Then he noticed the date on the calendar. "I'm in trouble," he whispered. He was way back into his own past, back before he even knew that he was quirkless. "Eri, did you do this?" he asked himself.
Fortunately it was easy to fall back into his life pre-UA, especially since Kacchan already had his quirk. Two months passed without a quirk showing up and Inko decided to take him to the doctor, who, as expected, declared him quirkless again. But this time, he reacted differently, so when Inko showed up, he had something different to say. "See that Mom? There's always a smile on his face, no matter how bad things get. Even when things seem impossible, he never gives up. That's the kind of hero I'm going to be when I grow up, even if I have to do it without a quirk," Izuku stated with full confidence. He had decided that this time, he would start preparing his body as early as possible in order to be able to better control One For All. There would be no rushing to prepare his body as a vessel this time, and with any luck, no permanent damage to his hands!
The next morning, Izuku started his training on YoTube by watching martial arts training videos. At every chance he got, he studied martial arts videos, from krav maga to shaolin. In order to try and keep his freindship with Kacchan and practice the arts he was learning, he took to challenging Kacchan to a game of Heroes vs. Villains once he believed he had mastered a lesson. Kacchan decided to start calling it a spar when he decided he was 'too old' to play the game. However, it had a different result than what Izuku had expected. Rather than repairing their friendship, it changed their relationship to respectful rivals ... though Kacchan still claimed superiority due to his quirk. Izuku also started redesigning his costume, starting with his last costume. Eventually he decided to honor All Might in a different way: by designing his own version of the Golden Age costume, done in Izuku's traditional green coloration though. Shortly after he turned eight, All Might vanished from the scene for months. Even though he knew what had happened, he was still in a near-panic mode until his mentor showed up again. When Izuku was ten years old, they drove by the Takoba beach and he saw how filthy it already was, he made a decision. "Mom, I want to clean the beach."
"Why, honey?"
"It's what a hero would do, Mom. Besides, how many people can't enjoy a beautiful beach because it's covered in garbage? I want to help them out." Inko actually smiled at that and agreed to help however she could. As nice as her abilities were though, Izuku wouldn't let her do anything besides drive him to the dump. Things continued like that for another three years until the fateful day of Mt Lady's debut.