Jubei Kibagami roams feudal Japan as a freelance swordsman. Following a past betrayal that left him without a master, he has lost all patience for warring political factions and their machinations. Unfortunately, his past and political intrigue converge when he encounters and rescues a female ninja named Kagero from a man capable of hardening his body to stone. As the sole survivor of her ninja clan, Kagero persists in her team's final mission: to investigate a mysterious plague that eradicated an entire village. Jubei intends to have nothing to do with this, but the stone-skinned man's allies, a group of ninja with supernatural abilities known as the Devils of Kimon, make that choice difficult. To complicate matters further, a government spy poisons Jubei, promising an antidote only if he uncovers the true intentions of the Devils of Kimon and their link to the plague. The investigation leads to shadowy leaders, a conspiracy to overthrow the government, and a man Jubei believed he would never encounter again.