@Anime_Lover6579
As a kid, the reader wanted to be a hero and beat villains with one punch. But, nobody believed or supported them because the reader was born Quirkless. Despite everyone trying to push them down, the reader sets up a harsh and unforgiving training regiment for the next three years to become the hero they dreamed of being.
Three years later, the reader is attending the UA entrance exam and naturally has everyone drop their jaws when they not only destroyed the robots but half the makeshift city for the exam.
It’s up to you if you want the reader to not be THAT strong, but I just thought it’d be funny if they were. Also, another idea is that some of UA could think that the reader cheated somehow (maybe even All Might could think the reader has connections with All For One?)