Jubei Kibagami is an itinerant swordsman-for-hire in medieval Japan. He has no sympathy for competing political factions and their ambitions because a previous betrayal left him masterless. Unfortunately, his background and political intrigue clash when he encounters and protects a female ninja named Kagero from a guy who has the capacity to turn his body stone-hard. Kagero, the solitary survivor of a ninja clan, continues her team's final mission: to investigate a mystery virus that wiped out an entire town. Jubei wants nothing to do with this, but the stone-like man's allies, a group of ninja with supernatural powers known as the Devils of Kimon, make that option difficult. To make matters worse, a government agent poisons Jubei and promises him an antidote if he survives.