Death was a character used by the Japanese Bard in his famous story A Tale of Two Sisters. In that story, he orchestrated the entrance of the Amakura sisters to Minakami Village, whereupon he summoned increasingly powerful ghosts in an attempt to deliver the girls to his clutches. Much to his frustration, however, the Camera Obscura allowed the elder twin, Mio, to fight off the ghosts. However, Death's final ghost, the Kusabi, though it was defeated by Mio, delayed her enough for Death to finish summoning the unstoppable Repentance, a mass of darkness which killed anything in its path.
To Death's surprise, however, Mio and Mayu were perfectly content to die by the Repentance if it meant dying together. Death, at this point, decided to cut his losses and took them across the River Styx, together.