Lone Wolf and Cub: Sword of Vengeance

Lone Wolf and Cub Sword of Vengeance Japanese or Kozure kami Kowokashi udekashi tsukamatsuru, literally Wolf with Child in Tow Child and Expertise for Rent is a 1972 film directed by Kenji Misumi, the first in a series of six. The film tells the story of Ogami Itt, a wandering assassin for hire who is accompanied by his young son, Daigoro.

As he walks in the rain, he remembers another rainy day several months earlier when his wife, Asami, was slain by three ninjas, ostensibly in revenge for Itts execution of a boy daimyo, but it was really part of a complicated plot by the shoguns inspector Bizen and the Shadow Yagy Clan to frame Itt for treason and take over the executioners post.Now a wandering assassin for hire, Itt takes a job from a Chamberlain, to kill a rival and his gang of henchmen, who pose a threat to the chamberlains lord. The chamberlain plans to test Itt, but a quick slash behind his back with his Dotanuki sword dispatches the chamberlains two men. The targets are in a remote mountain village that is home to hotspring spa pools. ........

Source: Wikipedia