imo, I’m pretty sure the teacher won’t save the girl once she hits rock bottom even though he’s offering to help her. To me it looks like he’s just enjoying everything falling apart.
I think sensei got too much trauma. he couldn't let this shit go and he couldn't act normal when bully happen.
but that girl is too stupid to notice about what kind of shit that might happen to her from now on. she probably won't say anything too anyone even if very horrible thing happen to her.