Yaiba Kurogane is an energetic young swordsman who's grown up training to be a samurai in the jungle with his father, Kenjuro. When they return to Japan, chaos seems to follow wherever Yaiba goes! Destined to be a legendary hero, Yaiba must learn to be a true samurai and save the world!

Yaiba, accompanied by the 400-year-old Musashi Miyamoto, and his friends Sayaka, Kagetora, and Shinnosuke, embarks on a training journey so he can defeat Onimaru. Now a demon, Onimaru has seized control of Japan and turned the parliament building into Onimaru Castle! His sights are set on Raijinken--Yaiba's Thunder God Sword--and he'll stop at nothing to take it!