The Testament of Sister New Devil Vol. 3 (manga)

With hardly a moment's rest since saving Mio from the White-Masked Demon, an even stronger enemy has appeared. As the timetable tightens on the new Demon Lord's reign, he'll stop at nothing to gain the power that resides in his predecessor's daughter. Just when it appears Basara, Mio, and Maria may've met their match, someone new arrives on the scene---a childhood friend of Basara, who is also from the mysterious hidden village of heroes!