Unsuccessful kamikaze aviator Ken Asuka transforms into a rugged, streetwise tough guy who resolves every issue through karate, until he discovers the famed swordsman Musashi Miyamoto in Eiji Yoshikawa's novels. Determined to emulate Musashi, he intensifies his karate training with relentless discipline. The story derives from a manga by Ikki Kajiwara and Jiro Tsunoda, which drew inspiration from Yasunobu Oyama's real life, the founder of Kyokushin Karate"s "hard‑knock" style in Japan's post-war tough era.