The Tokugawa shogunate maintains order, allowing the people to live in peace and relative prosperity. However, the dark side of the human heart never ceases to stir their greed: it serves as the ideal gateway for all demons that, by possessing humans, seek to enter their world. Exorcising these demons is the mission of Jonosuke, the master of keys. Renowned as Edo's finest locksmith, Jonosuke uses special locks to confine wicked spirits. With the aid of the enchanting O-kin, a divine who employs unorthodox methods, Jonosuke will encounter various notables of his era during his demon hunts; these figures will prove to be valuable allies when he must confront a plot targeting the highest levels of the state.