Kokubo-sensei is the head teacher at 's middle school. He also serves as the interim homeroom teacher of Hinata's third year class, 3A, whose female bullies are notorious for having driven their original to a breakdown, followed by her resignation.

Kokubo-sensei's effective first move to combat the psychological contagion which threatens to engulf the entire school is to disband its source, the gang of girl bullies, by reassigning each to a different homeroom.

Prior to relinquishing his post as class 3A's interim homeroom teacher, Kokubo-sensei has several philosophically interesting heart-to-heart talks with the recalcitrant lead bully, .