@churrystar
True. Their job is to discipline and guide these student into becoming good members of society. Kids are isolating and throwing things at someone… that should be troubling. I'm really disappointed at the teacher for letting that slide.
I think the red hair girl is probably the main bully. In the synopsis it mentions that Haji is being bullied by the most popular girl because of her childhood friend. The red headed girl is most likely the popular girl and therefore the head bully.
The childhood friend could be a girl or guy. It could be a cliche situation where Miss.Popular crushes on the childhood friend and bullies MC because she's jealous. Which just mean that the childhood friend is terrible. If you are the cause then own up and stop the mistreatment.
Or maybe her friend was originally the one being bullied and Haji tried to help her. This made the mean girl shift her target because someone tried to stand up to her. The childhood in this case would still be terrible but understandably so to some small degree. The friend probably is traumatised and is too scared to stand up for her friends.
Maybe her childhood friend is simply a terrible person. The friend could've set up the MC to be the target because the NC was different.