Kanzo Hattori, an Iga ninja, and his younger brother Shinzo are training in Tokyo. Kenichi, an elementary school student, lets the two of them stay and lives with them as if they were brothers, and one day he steals a picture diary written by Hattori (Kanzo). What was written there was that Shinzo became friends with a cute girl, Shinobino Ohime, and began to develop a relationship with Robomaru, a robot ninja of machine style ninja...