Samurai rebellion

During peace in 1725, aging swordsman Isaburo is living a henpecked life when his clan lord requests that Isaburo's son marry the lord's mistress, with whom he's displeased, even though she's born him a son. Isaburo wants to refuse, but his son Yogoro accepts the woman, Ichi, and they fall deeply in love. Their love renews Isaburo, so when the clan lord's elder son dies and the lord sends for Ichi to return to his side as mother of his heir, Isaburo opposes his lord. Yogoro and Ichi, who now have a baby daughter, stand with him. The clan orders their suicide, then sends soldiers to kill them. Isaburo's only hope is to take his case to Edo to expose the clan's cruelty.