Lucia Nanami is the main protagonist of the story and the mermaid princess of the North Pacific Ocean, keeper of the pink pearl. Seven years before the events of the series, she rescued a young boy who had fallen into the sea by giving him her pearl, and she later travels to the human world to retrieve it and complete her rite of passage to become an adult mermaid. She adopts the alias of a transfer student and enrolls in a coastal school, where she reunites with the boy, Kaito Domoto, and slowly falls in love with him.

Lucia is characterized by her simplicity, naivety, and a strong will, typical traits of a shoujo heroine. She is deeply caring, romantic, and always eager to help others, sometimes acting impulsively out of kindness. Her initial motivation is personal – finding her pearl and winning Kaito’s heart – but she soon learns of the danger threatening the marine world and embraces her duty as a mermaid princess. Her mission expands to gathering the seven mermaid princesses to summon the sea goddess Aqua Regina and defeat the sea demons that are attacking the underwater kingdoms.

Throughout the series, Lucia grows from an innocent, somewhat sheltered girl into a more responsible and courageous leader. In the first season, her story is largely a romantic comedy as she navigates unrequited love with Kaito while fighting enemies. The second season, Pure, tests her further when Kaito loses his memory after an accident and a new antagonist, Michel, appears. Lucia must protect the birth of a new mermaid princess, Seira, and withstand trials that deepen her bond with Kaito and her friends.

Her key relationships include her close friendship with the other mermaid princesses Hanon Hosho and Rina Toin, who support her in both battle and personal matters. She also shares a strong connection with her older sister figure Nikora Nanami, who guides her. The romance with Kaito Domoto is central to her character; he is drawn to her mermaid form but eventually comes to love her human self as well.

Lucia’s most notable ability is her transformation into her idol form, Pink Pearl Voice. As a mermaid, she can take on a human appearance, and during combat she transforms into a glittering idol to sing, using her voice as an offensive weapon. Her human form has dark blonde hair and brown eyes, while her mermaid form has lighter blonde hair and blue eyes, the most striking contrast among the mermaids. After completing a song, she often says the phrase Love Shower Pitch. She also has hobbies such as singing and making beaded jewelry.

Lucia’s development culminates in her embracing her role as a princess who must balance love, friendship, and the protection of the seas, ultimately fighting alongside the other mermaids to restore peace.