Nine-year-old Ren, having lost his parents, ran away from his guardians and wandered the streets of Tokyo. There he meets the great warrior Bear Cub—a bear-like monster who has come from a parallel world to find a disciple. Ren becomes that apprentice. In the world of monsters, the boy is given the name Devata and, under Medvezhut’s guidance, begins training to become a martial arts master.