High school girl Yaotose Hinako is living a quiet life in a seaside town, but she feels somewhat detached from her friends during the summer months when she is reminded of when her family died years ago. One day, she meets Shiori, a mysterious girl who reminds her of the ocean, especially when it comes to her translucent blue eyes, but Shiori soon reveals that she is actually a mermaid who has been looking for Hinako for a long time.