Lone Wolf and Cub: White Heaven in Hell (1974) on Netflix

Plot summary

Ogami Itto has survived every attempt the Yagyu clan has made on his life, and the Shogun now threatens Lord Yagyu Retsudo with disgrace over it. Retsudo's first answer is his daughter Kaori, skilled with flying daggers, sent to hunt the assassin and his small son Daigoro. He then turns to the Tsuchigumo, a hidden mountain clan whose members are said to practice black magic, led by Hyouei, a son born to Retsudo outside marriage who has his own reason to want the Yagyu brought down. Hyouei sends his three most feared followers, who can tunnel through the earth, after Itto and Daigoro, and they kill anyone the pair meets.