When Toujo Basara, a first-year high school student, is unexpectedly informed by his father that he will be gaining two step-sisters, panic ensues. Little does he know, the beautiful Mio and Maria are actually the Demon Lord and a succubus in disguise. A mishap leads to Basara becoming their master instead of a servant, thrusting him into a world of chaos. As he navigates ecchi encounters and demonic threats, Basara must protect Mio from rival demon and hero factions. Prepare for a thrilling action drama as the unlikely trio faces their destiny together.