Mr. Sengoku

Akito's homeroom teacher in middle school. Sengoku despises Akito and picks on him relentlessly. He believes Akito is a violent and dangerous boy by nature and cannot be changed. Akito, on the other hand, pegs Sengoku as the unfair and spiteful person he is, and refuses to curry Sengoku's favor. Sengoku hits Akito, but will not admit it, and tries on several occasions to get Akito expelled. Thus, making Sengoku the main antagonist in Kodocha's second season.

(Source: Wikipedia)