Ibuki makes a big decision on the eve of his graduation and invites Yuri to walk home with him. Since he will attend college abroad, this will be the last time he will see her. Determined to confess his long-standing love for her, he gathers his courage, only to be interrupted by dire situations. However, those are the least of his priorities right now.

Toshihide's greatest treasure is an abandoned underwater piano. Playing it allows him to feel connected to his mermaid mother. One day, he meets the mermaid Shiju. She has been secretly listening to his performances and happens to save his life. When he offers to teach her the piano, they soon become good friends. However, mermaids are terrifying creatures that feed on human beings.