Nounashi Miko Wa, Kishin-Sama Ni Aisareru

Sayo is shunned as the "incompetent shrine maiden," due to her lack of spiritual power despite being of a shrine maiden's lineage. One night, when Saya is about to be attacked by a youkai, she is rescued by Akatsuki, the fierce god she reveres. Her younger sister, Nanase, who succeeded the shrine maiden's role in place of Saya, heard about it, and Saya is offered as a sacrifice as the "Bride of the Fierce God". During her sacrificial ceremony, Saya tries to escape in her bridal dress. The one who appears as she is in the midst of this is... (from mangaupdates)