The action of the animation movie takes place in parallel worlds — in the world of people and the world of monsters. Nine-year-old boy Kyuta lost his mother, and he never knew his father, but he doesn't want to live with official guardians, therefore he runs away from home. Wandering the streets of Tokyo, the boy meets a werewolf bear Kumatetsu, who takes him to a unique world where monsters live.
In this world, the lonely Kyuta meets interesting creatures in which there is not a drop of darkness. Practicing martial arts under the supervision of his new teacher Kumatetsu, the boy no longer feels lonely. Every day, the complex relationship and misunderstanding between the boy and the monster are on the decline, and the difficulties are replaced by understanding, support and friendship.