Hands down. Sensei is best girl. She is crazy af but loyalty shows no ends, willing to live with all 3 of them together, plan on going ride or die with mc, and has strong determination. She is such an interesting character.
Did she fuck up her life in having a relationship with her student? Yes.
Not a single character is innocent in this manga (except Essomori's ex gf) and it's amazing how morally grey they are.
A lot of shades of grey.They're a pretty dark grey!