I don't know for sure as it depends on the specific fanfic. It could be a main character from the original My Hero Academia series who is put in a new and difficult situation that makes them 'broken but not defeated'.
There are many possibilities. It could be a pro - hero who has fallen from grace due to a false accusation. This hero would be broken by the loss of their reputation and public support. However, they are not defeated and strive to clear their name and regain their status. Another option could be a student at U.A. High who has a family crisis that makes them feel broken. Despite this, they find strength within themselves and from their friends at school to keep going and not be defeated by their personal problems.