Kiru

Master swordsman Raizo Ichikawa comes home to find his sister dead and his father dying. Before that happens, he is old a long story about how his real mother assassinated her husband's evil mistress, fled with a samurai, and was captured by by her clan. No one would kill her, so it fell to her lover, who gave him to the man Ichikawa thought was his father.

It'ss one of those weird movies that the Japanese enjoyed back then, in which people do horrible things to seek vengeance in beautiful surroundings where the birds chirp. It's directed by Kenji Misumi, who would begin directing the Zatoichi series that very year. It's quite lovely and quite alien to my understanding. Perhaps you will get more out of it than I did.