In the Edo period of Japan, in the year 1725, Isaburo Sasahara (Toshiro Mifune) is a vassal of the ''daimyō'' of the Aizu clan, Masakata Matsudaira. Isaburo is one of the most skilled swordsmen in the land, whose principal rival is his good friend Tatewaki Asano (Tatsuya Nakadai). Isaburo is in a loveless marriage with a shrew of a woman. One day, one of the daimyo's advisors orders Isaburo's elder son Yogoro (Go Kato) to marry the daimyo's ex-concubine, Ichi (Yoko Tsukasa), even though she is the mother to one of the daimyo's sons. With much trepidation, the family agrees. In time, Ichi and Yogoro find love and happiness in the marriage and a daughter, Tomi, is born.