Ep. 4: The Lonesome Princess

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A new sea demon, Yuri, appears during a concert given by Taro and uses her music to hypnotize the attendees and attack the mermaid princesses, who are also there. Rina reveals herself to be the mermaid princess of the North Atlantic and then makes acquaintances with Lucia and Hanon. The three mermaids become known as the trio teen idols. (Source: Wikipedia)