After failing as a kamikaze pilot, Ken Asuka turns into a rough, tough hooligan who resolves all his problems with karate, until he discovers the legendary swordsman Musashi Miyamoto in the novels of Eiji Yoshikawa. Determined to live his life like Musashi, he starts to take karate more seriously. Based on a manga by Ikki Kajiwara and Jiro Tsunoda, which was itself inspired by the real life of Yasunobu Oyama, the founder of the "hard-knock" Kyokushin Karate school.