Manji is a notorious swordsman in medieval Japan known as the "Hundred Man Killer" for killing one hundred innocent men. However, there is something considerably more terrifying than his gloomy reputation: he is immortal. This is the work of Yaobikuni, an eight-hundred-year-old nun who implanted bloodworms capable of mending practically any wound in Manji's body. Manji decides to kill a thousand bad persons in order to atone for his misdeeds. Yaobikuni agrees to this idea, stating that if he is successful, she will remove his curse of immortality. Soon after making this pledge, Manji encounters Rin Asano, a 16-year-old girl who asks Manji for help in murdering those who murdered her parents.