An OVA that was bundled with the seventh volume of the Shinmai Maou no Testament manga.

What’s the best way to celebrate a birthday? Well, to the succubus Maria, there’s only one thing to do—get Mio and Basara to hook up! Using the guise of Mio’s birthday, and a lust spell, she’s determined to have the perfect setup for a sexy celebration.

(Source: Funimation)