First year high-school student, Toujo Basara, is now living with two beautiful step-sisters thanks to his eccentric dad. But Mio is actually the new Demon Lord and Maria's her succubus chaimberlain. Throw in a "reversed contract", rival demon tribes, and the ecchi situations mainly brought on by Maria for good measure, and you have a situation where Basara's life will never be the same. This seinen adaptation of the light novel mostly focuses on the said latter ecchi situations that occurs between the three main characters.