Japan, sometime in the near future where a group of shinobi have been brought together and trained to deal with the demon threat that has persisted for some time. It has long been the case that demons and humans avoided each other, but that belief is about to be destroyed.

Erin is a mercenary who was once on the brink of death, but saved by Nighthawk a sword spirit. Since then they have been traveling together, this is the story of these two.