Hinako, a high school student haunted by a troubled past, lives alone in a quiet seaside town, burdened by a constant feeling of drowning. Her monotonous life changes when she is attacked by a monster and rescued by a mysterious mermaid. But the mermaid's protection comes with a chilling condition: she intends to devour Hinako once she has matured into the perfect meal. As an unusual bond develops between predator and prey, Hinako finds herself drawn to the very creature destined to consume her.