When a pair of sexy girls, Maria and Mio, come to live with high school student Basara Toujou, his life changes forever. These two ladies have secrets that they don't keep for long-Maria is a succubus, and Mio is a future Demon Lord. But Basara has a secret of his own-he's the last descendant from a clan of demon-fighting heroes. So, what happens when you put a succubus, a demoness, and a demon-fighting hero under the same roof? They form a bond that will help them take on anything!