Based on the video game series, Shiro Tokisada Amakusa, an evil entity from beyond the grave, decimates the countryside in the name of Ambrosia. One of the victims of his attacks was the parents of a boy named Otsuna. He seeks revenge with his Kusudaryugan sword techniques. Along the way, he meets Haohmaru, who mainly chooses to ignore the devastation in the country. However, after he witnesses how twisted the populace has become, he mends his arrogant ways and goes to slay Amakusa.