Ep. 4: Yuri hypnotizes concertgoers while Rina reveals her identity to Lucia and Hanon.

4

During a concert featuring Taro, a new sea demon named Yuri appears and uses her music to hypnotize the audience. She then attacks the mermaid princesses present at the event. Rina reveals herself as the mermaid princess of the North Atlantic. Following this confrontation, she makes acquaintances with Lucia and Hanon. The three mermaids subsequently become known as the trio teen idols. This episode establishes their new public identity and introduces the threat posed by Yuri's hypnotic abilities against the mermaid community.