Three boys, Kotarou, a ninja in training, Rikiya, a training baseball player and Yousuke, a studiying scholar were living normal lives in Blue Sky City. One day, Kotarou along with his father Toubei accidentally broke the seal that links the Demon World from the Human World. Until Eldoran, the spirit of light in the Demon World appeared in front of Kotarou, Rikiya and Yousuke…