Once, the land of Togenkyo was a peaceful land, where humans and yokai lived together. Then, however, men appeared who tried to revive Gyumaoh, the Great Yokai who was slain by the war god Nataku Taishi and buried in Houtou Castle 500 years ago, by using a forbidden combination of chemistry and magic.
The negative energy waves this created spread across Togenkyo, causing the yokai to go insane and attack humanity. To save the land, Kanzeon bosatsu orders Son Goku, Genjyo Sazno, Sha Gojyo, and Cho Hakkai to go west. The four set out on a journey to stop the experiment to revive Gyumaoh.