When a pair of sexy girls, Maria and Mio, come to live with high school student Basara Tojo, his life changes forever. The two girls have a secret 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. They come up with creative ways to resolve their differences.