After his mother's death, Miwatari Yuu returns from Tokyo to live with relatives in the city of his birth, Ousuku. Yuu is the latest of a line of Shinto priests that stretches back generations. After his arrival, he runs into a strange girl who seems to be searching for the Northern Lights. Yuu saw the Aurora as a child, though no one believed him, and his mother had told him it was the armor of the Valkyries traced across the sky. Yuu's destiny is interwoven with this mysterious girl and the aurora, and he will not be able to help being drawn into a battle that involves both gods and humans!