In reading over some older rps, I've gotten the urge to play a student making another student his. I'd play the new girl in a rough school who catches your character's eye. Reputation is everything in this school and there's much illegal activity going on in the school. (drugs, sex, underground racing/gambling, etc.) Teachers are also involved in the illegal activities and its a well known fact the police and mayor are also involved which is why its allowed. Its by chance the sweet good girl ends up at this school as her father gets transferred there by his company. He of course has no idea of the school's activity and is assured by the principal, possibly kin to your character and thinks the girl will be perfect for his nephew after seeing her, that the school is a good school.
Your character decides to make her his after getting the information about her from his uncle and seeing just how beautiful she is. This will start off as non con, but she will soon see being his actually protects her from others and she eventually falls for him. He has his reputation to uphold but he starts to fall for her as well and will do whatever it takes to protect her at all costs from the other kids in the school.