Just came up with this:
A Danny Phantom/Boku No Hero Academia crossover AU where after cleaning up Freakshow’s worldwide mess at the end of Reality Trip, residual traces of ectoplasmic energy from the Reality Gauntlet are present in the air around the world. Then, when Danny tries to destroy the Reality Gauntlet (which isn’t fazed considering how powerful an artefact it is) back in Amity Park, it backfires and sends out an ectoplasmic reaction that traverses the entire planet and bends reality, leading to the emergence of Quirks.
Amity Park is thrown into a stasis in the Ghost Zone for just over 200 years by the Gauntlet’s backfiring, until All For One (in an experiment carried out just before the League of Villains is formed), tried to wrench Amity Park out of its stasis and brings Danny, his friends, family, classmates and the rest of a group of people from Amity Park into hero-society Japan one year before BNHA canon. They end up out of the villain’s clutches and try to make it on their own in the strange society.
Danny wants to keep heroing now that the people who know him found out his secret identity while escaping All For One, and the new society doesn’t ostracise superheroes; but when wiping the worldwide reveal of his secret identity in RT he wiped all records of his hero alter ego’s existence outside of Amity Park, so he can’t become a hero legally. His birth records say he is from another country and over 200 years old, so he can’t exactly let them be found by authorities, and there is no evidence of his superhero record to prove to the law that he was a superhero from before the dawn of pro-heroes. He has to become a vigilante, until he bumps into All Might numerous times, they confide in each other about their true identities and superpowers and Danny is given the chance by All Might to explain his circumstances to Nezu and UA (because they’d believe him; they’ve dealt with weirder shit than the Government has and can keep the secret of his birth records under wraps). He gets the chance to go to UA, given that his year of Japanese language practice is adequate enough to get started. He probably meets Midoriya when All Might forces them to train, because Danny relies on his powers too much and is physically unfit.
Obviously when Danny gets into UA he replaces Mineta in the top class.
