In feudal Japan, Manji, infamous as the 'Hundred Man Killer' for his deadly past, carries a darker secret - immortality bestowed by a centuries-old nun. Seeking redemption, he vows to slay a thousand wicked souls to break his curse. When 16-year-old Rin seeks his aid in avenging her parents' murder, Manji initially hesitates before accepting, pledging four years of protection. United by a shared quest for justice, they venture forth, bound by a destiny of retribution, forgiveness, and self-discovery.