Who Is Manji?
Manji was a samurai in the service of the hatamoto Horii Shigenobu. When he discovered his lord's corruption he killed him, and became an outlaw with a name earned in the fighting that followed: the Killer of 100. Among the hundred were men he had no quarrel with, including his own brother-in-law, and the death of his sister Machi, the one person he had left, finished what was left of him.
Then the 800-year-old nun Yaobikuni gave him the kessen-chu, the sacred bloodworms, and dying stopped being available. Manji's bargain with her frames the whole series: to earn his mortality back he must kill 1,000 evil men, one for every ten he wronged. It is why an immortal with no reason to care hires himself out as a bodyguard to a teenage girl: Rin Asano reminds him of Machi, and her war is the first work that fits the debt.