Nounashi Miko wa, Kishin-sama ni Aisareru

Sayo was born to be the next protector of her village, but her lack of spiritual powers earned her the nickname "worthless shrine maiden." One night, she is attacked by yokai when the demon god Akatsuki, who is worshiped by the village, comes to her rescue. Nanase, her younger sister who became the shrine maiden in her place, hears of this and demands that Sayo be sacrificed as the "Bride of the Demon God." The sacrificial ceremony begins, and Sayo, dressed in the bridal kimono, makes a desperate attempt to escape when in her moment of need, a familiar figure appears... (Source: MangaPlaza)