A new school term begins; Hiroshi's heart is attacked by a Yōkai, so Nube mus...
Jigoku sensei Nube
Season 1 Episode 5: Gakkou no shichi fushigi Ma no 13 kaidan (The school's Seven Mysteries - Demon of the 13th step)
Katsuya meets a troubled boy who makes him cross the 13th step.