In feudal Japan, Manji, known as the 'Hundred Man Killer' for his deadly reputation, harbors a chilling secret - immortality gifted by a centuries-old nun. Seeking redemption, he vows to slay a thousand evildoers to break the curse. When he crosses paths with Rin Asano, a girl seeking justice for her slain kin, Manji initially hesitates but ultimately pledges to safeguard her for four years. Together, they venture into a world of retribution and renewal, bound by a shared quest for absolution.