While performing in a movie at Toei Eigamura, Kinnikuman suddenly disappears. Somehow, he has been sent to Edo Period Japan. In Edo Japan, a villain called Shuten Douji (朱天童子) is threatening to destroy the Earth if he is not given Princess Mari. Always willing to impress a pretty girl, Kinnikuman immediately vows to destroy Shuten Doji. He disguises himself as Princess Mari and goes to meet Shuten Doji, but Shuten Doji and his Big Four (四天王, Shitennou) see through Kinnikuman’s disguise and beat him up. Aware of Kinnikuman’s situation, Terryman, Robin Mask, and the other Seigi Choujins travel to Edo Japan (via Kinkotsu-obaba’s powers).

(Source: Kinnikuman Wiki)