The premise is extremely stupid and feels made by someone that has never interacted with people their whole life. Just because you act like a decent human being you shouldn't expect and should not receive a harem, the world doesn't work that way, the girls even think he is a hero for doing the bare minimum of what a good samaritan should do, this kind of stories is why "nice guy syndrome" exists, I find more believable isekai stories where the MC gets a harem for defeating dragons with his dick or something than this kind of bullied teenager's wet dream...