In the past 11 episodes I watched. Well heres a fact that we know
now from the anime, Reiko paints pictures. So that could mean that she is also Mikami-sensei. Mikami-sensei is an art teacher, right? Reiko likes art so that means that she could be Mikami-sensei. She could teach art at school while being an art teacher. Also Mei asked Kouichi if Reiko paints or not. This proves that Reiko = Mikami. Having the same hobbies proves that Reiko = Mikami.
Picture Below proves it Left - Reiko : Right - Ritsuko
