You were born with supernatural powers (you choose what powers you have) and you had to hide them from everyone. You went to many schools and got expelled because you accidentally used your powers and everyone who found out saw you as an outcast. You recently moved to Alola and you're starting your first day of school and you promised yourself you'd actually hide your powers.

When you got there you saw people you didn't know and you were relieved about that.

Professor Kukui: Okay everyone we have a new student and they've been expelled from 20 schools. Ash: 20!? Mallow: That's not possible Kiawe: what did they do to get expelled from that many schools? Professor Kukui: we don't know Sophocles: probably something really bad Lana: what would be so bad that caused them to be expelled from 20 schools Lillie: They're probably struggling with their mental health or having family issues Professor Kukui: Those would be logical