Millennia ago, Mother was an ancient water deity who was imprisoned below the earth upon the creation of light. Mother's mate, Otoshigo, fled to the depths of the ocean. Over time, Mother has been determined to return to the surface, and has sent out avatars (possessed human beings whom she controls) to prepare for her return. However, they continually fail their mission, and never return to the Underworld. In 1976, an underwater cable was cut, and all power to Yamijima Island was lost. Four-year-old Shu Mikami finds a young woman washed up on the shore. The woman, Kanae, bears an extraordinary resemblance to Shu's dead mother. The two become inseparable and Kanae moves in with Shu and his father. The Yamijima locals fear her because of her aversion to sunlight. Kanae is actually an avatar of Mother, tasked with manipulating Shu into opening the seven gates of the Underworld, which are located on Yamijima Island, and keep Mother imprisoned. Before Kanae can complete her mission, Tsuneo Ohta, the head of a group of fishermen, determines she must be killed.

Millennia ago, Mother was an ancient water deity who was imprisoned below the earth upon the creation of light. Mother's mate, Otoshigo, fled to the depths of the ocean. Over time, Mother has been determined to return to the surface, and has sent out avatars (possessed human beings whom she controls) to prepare for her return. However, they continually fail their mission, and never return to the Underworld. In 1976, an underwater cable was cut, and all power to Yamijima Island was lost. Four-year-old Shu Mikami finds a young woman washed up on the shore. The woman, Kanae, bears an extraordinary resemblance to Shu's dead mother. The two become inseparable and Kanae moves in with Shu and his father. The Yamijima locals fear her because of her aversion to sunlight. Kanae is actually an avatar of Mother, tasked with manipulating Shu into opening the seven gates of the Underworld, which are located on Yamijima Island, and keep Mother imprisoned. Before Kanae can complete her mission, Tsuneo Ohta, the head of a group of fishermen, determines she must be killed.