Kotetsu Miyasaka, a first-year high school student with an exceptional talent for kendo, shares his passion for the sport with his younger brother, Yayoi. Having always lived in Kotetsu's shadow, Yayoi enrolls in a different school than his sibling, where he now attends school with second-year kendo prodigy Chihiro Kawase. But with an important kendo tournament around the corner, Chihiro threatens Yayoi to tamper with his brother's shinai—a wooden sword used for kendo—to ensure Chihiro's victory. When Yayoi fails to comply and comes home with bruises, Kotetsu, brimming with rage, challenges Chihiro to a fight using steel swords. However, amid the scuffle, Kotetsu traverses through time to the Bakumatsu era, the final years of the Edo period.

Unsure of who is friend or foe, Kotetsu is taken into custody by Souzou Sagara, the head of a band of roushi. Seeking Kotetsu's strength, Sagara asks him to join his group and change the world together. As if life in the Edo period were not chaotic enough, Kotetsu is met with familiar faces of his own era but with completely different identities. As he joins forces with Sagara, he must survive in this perilous era while contributing to the history of ancient Japan.