Following a tragedy that claimed her family's lives in the sea, Hinako Yaotose is haunted by thoughts of herself sinking into the ocean forever. With Miko Yashiro as her sole companion, she maintains a half‑happy front, yet whenever Miko departs, hopelessness swallows her. Everything shifts one summer when she encounters a mysterious girl whose eyes mirror the depth and clarity of water, pulling Hinako in like nothing else has for ages.
While aimlessly searching for the stranger, Hinako is abruptly dragged beneath the waves by a monstrous deep‑sea beast; she awakens to find the girl—Shiori Oumi—who morphs into a creature and slays Hinako's attacker. Despite this brave deed, Shiori"s motive remains the same as any other monster: to devour Hinako.
The next day, Shiori steps into Hinako"s classroom as a new transfer student, and Hinako cannot help but grin—finally, someone who could grant her silent wish for death has arrived. Her presence shrouds the room in an uncanny calm, and Hinako feels a strange relief today.
