Hiroshi Ichikawa, an orphan, lives with his older sister Utako in the Japanese apartment building Arama-sō. After their parents' loss, Utako takes responsibility for his care and daily needs.

He befriends Kaibutsu-kun, the prince of Monster Land, when Kaibutsu-kun and his companions—Dracula, Wolfman, and Franken—relocate to the human realm and move into Hiroshi's neighborhood, leading to their ongoing association. Hiroshi becomes involved in their conflicts against antagonistic forces, primarily the demon group Demonish and its assassins.