A Shogun who grew paranoid as he became senile sent his ninjas to kill his samurai. They failed but did kill the samurai’s wife. The samurai swore to avenge the death of his wife and roams the countryside with his toddler son in search of vengeance.
In the third film of the Lone Wolf and Cub series, Ogami Itto volunteers to be tortured by Yakuza to save a prostitute and is hired by their leader to kill an evil chamberlain.