After the first season's truce, Basara Toujou travels to the Demon Realm with his step-sisters Mio Naruse and Maria Naruse, where Mio has to claim her birthright as the daughter of the late Demon Lord Wilbert. The moderate faction that backed Wilbert is under siege from Leohart's current council, and Basara fights through a gauntlet of high-ranking demons to keep Mio's standing intact. At the same time the master-servant pact binding Basara and Mio deepens, tying their powers together as the struggle for the Demon Realm turns violent.