Basara Toujou lives with his step-sisters Mio and Maria Naruse, demons bound to him by a master-servant pact that keeps dragging the household into compromising situations. In this OVA, bundled with the manga and tied to the BURST season, the succubus Maria turns Mio's birthday into a scheme to push the two of them together. A self-contained comedy side story, not a standalone entry point.