S1E5: Mermaid Rhapsody

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.