Yaiba lives with his father, Kenjurou, in the forest. One day, while Yaiba was eating, a troop of gorillas came to attack. Yaiba and his father escaped and hid inside a box, but they didn't know that the box was full of pineapples and was going to be transported into the city. In the city, Yaiba finds out that he is a legendary warrior and has to fight the evil of a demonic looking high-school student named Takeshi Onimaru.