Ever since losing her parents and older brother at a young age, Hinako Yaotose has been living a hollow life, as if her mind remained sunk in the deep sea. She hopes that summer — a season that brings back her sad memories — will end soon.
One day, when Hinako is waiting for her only friend Miko Yashiro, who has been kept after school, she feels the presence of a girl with the scent of the ocean. Following her feeling, Hinako, still wearing her indoor shoes, heads for the seaside, and is drawn into the sea by a non-human creature that suddenly appears from the sea. When Hinako closes her eyes while thinking that she can reunite with her families, rather than being scared, she is saved by a mermaid girl named Shiori Oumi.
Shiori tells Hinako that her flesh and blood are so delicious that many kinds of yokai, including Shiori herself, are attracted to her. Then Shiori promises that she will protect Hinako from other yokai until Hinako matures to a perfect state, at which point, she intends to eat Hinako.

An earnest thought crosses Hinako’s mind that Shiori could grant her wish.

This is a beautiful, bittersweet story set in a seaside town modeled after Iyo, Ehime which begins with the encounter between Hinako, a girl who has a wish to die, and Shiori, a mermaid who desires Hinako’s flesh and blood.