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Sara

Sara is the Mermaid Princess of the Indian Ocean and keeper of the orange pearl. She joins Gakuto in his quest to take over the marine world after an incident bestowed her a dark power, turning both her orange hair and her orange pearl pitch black (though her eyes stay orange) and destroying her own kingdom. That incident was a proposed rendezvous with Tarō, her secret human lover, in which he never showed up. (In the manga, he actually arrived before, but Sara's guardian found out about the relationship and insisted that he leave, convincing Sara that he had abandoned her.) In a fury, Sara unleashed a wave of power, destroying her kingdom and causing the wave which killed Kaito's parents and from which Lucia saved Kaito. In the manga, her villain name is Black Pearl Voice and she transforms into an idol in a black dress reminiscent of a diva. However, in the anime, she does not transform until she turns good, and instead has the power to sing offensively in a humanoid, amphibious form like the villains and mermaid idols, with or without her E-pitch. In the end, she decides to join the other mermaids as is her duty. She, herself, seals the gate to Gakto's castle in the book because it's her duty and she unsealed the gate after her kingdom was destroyed. In the TV show, Aqua Regina seals the gate and Sara goes with Gaito because she loves him. She also appears in the second season as a spirit, informing Lucia of the future Orange Pearl Voice and offering her assistance where she can. Sara is also seen singing with the other mermaid princesses in the very last episode of Mermaid Melody Pichi Pichi Pitch Pure.

Coco

Coco is the Mermaid Princess of the South Pacific Ocean and keeper of the yellow pearl. She is incarcerated by the sea monsters for most of the first season, so not much is known about her. In the manga, however, she is a friend of fellow Mermaid Princess Sara. Later, she found to be playful and gentle in the manga, yet brash and outspoken in the anime. Her idol form is Yellow Pearl Voice.

Caren

Caren is the Mermaid Princess of the Antarctic Ocean, keeper of the purple pearl, and twin sister of Noel. In the anime, she first appears as the winner of a beauty contest that the main trio enters; in the manga, she first appears to save them from the Dark Lovers. In the first season, Tarō asks her about his mermaid, and she later blames Rina for Noel's kidnapping. Even after things are straightened out, she chooses to go find Noel alone. She is Noel's polar opposite, having a mysterious personality. While she is cold and distant in the first season, she is found to be wild, humorous, and even a bit strange in the second. Her idol form is Purple Pearl Voice.

Noel

Noel is the Mermaid Princess of the Arctic Ocean and keeper of the deep blue pearl. She helped Rina escape from the sea monsters, which led to her capture. She is calm, gentle, caring, and studious. Her idol form is Ai-iro (Deep Blue) Pearl Voice.

Luchia Nanami

Luchia (or Lucia), is the Mermaid Princess of the North Pacific Ocean, keeper of the pink pearl, and the main character of the story. She goes up to land to search for a boy she saved seven years ago. She is unaware of the danger in the marine world and of her real mission until she is told of them by her "older sister", Nikora. She is characterized by her simplicity and naïveté, but with having a strong will, typical traits of shōjo manga heroines. Her idol form is Pink Pearl Voice. Of all the mermaids in the series, Lucia's mermaid form and human form contrast the most (Luchia has dark blonde hair and brown eyes in the surface while having lighter blonde hair and light blue eyes while at sea).