Failed kamikaze pilot Ken Asuka becomes a rough, tough hooligan who settles all of his problems with karate, until he learns about the legendary swordsman Musashi Miyamoto in the novels of Eiji Yoshikawa. Resolving to live his life like Musashi, he begins to take karate more seriously. Based on a manga by Ikki Kajiwara and Jiro Tsunoda, itself inspired by the real life of Yasunobu Oyama, the founder of the "hard-knock" Kyokushin Karate school.