Phantom of the Toilet(1995)

トイレの花子さん

Set in an elementary school and centered on a boy named Takuya and a new transfer student named Saeko. Takuya's classmates think that Saeko has been possessed by Hanako, the ghost that lives in the bathroom. The rumor is especially encouraged by a girl who has a crush on Takuya and is jealous since Takuya likes Saeko.