Luchia (七海 るちあ Nanami Ruchia) 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 her pearl which she used to save a boy named Kaito seven years ago. Later in the series, Luchia and Kaito become lovers. 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. In the Pure season, Seira, is about to be born as well, waiting to meet Lucia. Lucia now has the job of retrieving all the pieces of her heart contained in Michel's feathers. Overall, no matter what the situation, she never gives up hope. Her idol form is Pink Pearl Voice. Of all the mermaids in the series, Luchia's mermaid form and human form contrast the most (Luchia has short dark blonde hair and brown eyes in the surface while having long lighter blonde hair and light blue eyes while at sea). Luchia is the first Mermaid Princess to transform into her idol form. Some western fans spell her name with an "h" due to a misunderstanding of the spelling systems of different languages. The Italian name, Lucia, follows Italian spelling rules, which say that "c" is pronounced as a post-alveolar affricate (the same sound that is written as "ch" in English) when it appears before a front vowel (in this case, "i"). That pronunciation is correctly represented in Japanese kana as るちあ. When attempting to transliterate the kana back into Latin characters, some people, unaware of the Italian spelling of the name, tried using the English "ch" to represent that consonant, resulting in the incorrect spelling "Luchia".
Hanon Hosho (宝生 波音 Hōshō Hanon) is the mermaid princess of the South Atlantic Ocean, keeper of the aqua pearl and the deuteragonist of the series. She is Luchia's best friend, but fights with her like any teenage girl. Unlike Lucia, Hanon goes up to land to escape water creatures like when she grabs the bandana off of Eril's head. She is perky and feminine and a bit more worldly than Luchia, although she tends to be lazy in cleaning. This worldliness is evidenced by many of her actions—especially by her romantic pursuit of her music teacher, Tarō Mitsuki. In the Pure season, she develops an interest in a boy, Nagisa. She also likes to share things with him like ice cream. Her idol form is Aqua Pearl Voice, although the first time that it is named in the manga, she is erroneously called Blue Pearl Voice.
Rina Toin (洞院 リナ Tōin Rina) is the mermaid princess of the North Atlantic Ocean, keeper of the green pearl and the tritagonist of the series. During school, she wears the boys' uniform instead of the girls. Initially she is depicted as beautiful but stern and bent on revenge for the capture of her best friend, Noel. Later, however, she evolves into a more mature character, and acts as an older sister figure to Lucia and Hanon. She seems to love plasma TVs and shows this love in many anime episodes. In the Pure season, she becomes close to a boxer, Masahiro. She also seems to love watching comedy shows. Her idol form is Green Pearl Voice. Some fans in the West still spell her name as Lina, because the Japanese language does not distinguish the sounds "r" and "l", treating them as the same. This means that "ri" and "li" are both represented as リ, and it can be difficult to figure out what the intended romanization is until it is established by official sources.
Karen (かれん Karen) is the mermaid princess of the Antarctic Ocean (sometimes known as the Southern Ocean), keeper of the purple pearl and one of the supporting characters of the series. She is the 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. Caren and Noel are twins, born on opposite sides of the Earth. When Karen finally meets Noel, she launches herself at Noel, hugging her and calling her Onee-sama, a respectful term for big sister. Even though the two had not met before, Karen cares most for Noel and would do anything to save her, even if it meant Karen having to find her on her own. 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. Karen finds a love interest, Subaru. Her idol form is Purple Pearl Voice. Some fans refer to Caren's name as Karen.
Coco (ココ Koko) is the mermaid princess of the South Pacific Ocean, keeper of the yellow pearl and one of the supporting characters of the series. She is incarcerated by the sea monsters for most of the first season, so not much is known about her other than that she is a friend of fellow Mermaid Princess Sara. Coco normally worries for her friends, especially Sara and can keep their secrets very well. She is a bit flirt but doesn't have any relationships with boys in the manga and anime. Her idol form is Yellow Pearl Voice.
Noel (ノエル Noeru) is the mermaid princess of the Arctic Ocean, keeper of the indigo pearl and Karen's big twin sister. She loves to read books and is a good friend of Rina. She helped Rina escape from the sea monsters, which led to her capture. She is calm, gentle, caring, and studious (as she sometimes wears glasses on land later in the second season of the anime). She is Caren's older twin sister by about a minute at the most. Noel cares deeply for Caren, the one that she had always wanted to meet. Her idol form is Indigo Pearl Voice. In the third volume of the English manga, ai-iro was translated as indigo, but deep blue makes more sense regarding the character's colour scheme; the colours may be based on the rainbow, but Lucia is pink, not red. Some refer to Noel's name as Noelle, because originally Noel is a male name, while Noelle is the female form, but the official English translation as well as the official Japanese romanization uses Noel.
Sara (沙羅) is the original mermaid princess of the Indian Ocean, keeper of the orange pearl and a character who makes love on the opposite sides. She joins Gaito 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 microphone. In the end, she decides to join the other mermaids as is her duty. She, herself, seals the gate to Gaito'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 and as a result, they die. The manga shows that she goes with him because she realizes that he is the one that needs her the most and that what he did was partly out of love for her and the want to make her happy. 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.
The Dark Lovers
The Dark Lovers (ダーク・ラバーズ Dāku Rabāzu) are Gaito's four female followers who serve him in exchange for his love for them. There are composed of the following:
One of the Dark Lovers. Izul (イズール Izūru) is the most mature of the four, she has the power to control waves and marine beasts and has the ability to create dragons from water. She is also the most obsessed with winning the heart of Gaito. In her Water Demon state, she has the appearance of a mermaid.
The Black Beauty Sisters
They are composed of the red-wearing older sister Sheshe (シスターシェシェ Shisutā Sheshe) and the blue-wearing younger sister Mimi (シスターミミ Shisutā Mimi). Gaito hires them after the Dark Lovers' failed attempts to capture the Mermaid Princesses. These two have the ability to sing tunes more powerful than the songs the Mermaid Princesses themselves sing, although in the anime and the second arc of the manga, the Princesses manage to get strong enough to overpower them. Though Gaito turned them back to their original forms (two anglerfishes), they are brought back in the second season after being revived by that season's antagonist, Michel, and made them his servants. It has been shown that Mimi has a human form whose hair gets longer and wears glasses over her brown eyes. She befriends with Lucia, Hanon, and Rina. Once Mimi learned of their mermaid identities she now hesitates to capture them.
Kaito, the son of a pair of musicians, is an avid surfer, as well as Lucia's love interest. Though he is popular with girls, he is secretly in love with a beautiful mermaid who saved him from a shipwreck seven years ago (caused by Sara when her pearl went out of control), and has yet to realize that this mermaid is Lucia. Kaito kept Lucia's pearl in a necklace until he gave it back to her. Later in the story, it is discovered that beneath Kaito's human exterior lie some distinctively inhuman qualities and that he is the prince of an ancient water race called Pantharassa and is the younger twin brother of Gaito. Aqua Regina separated Gaito and Kaito to prevent world chaos. Kaito has a hard time when Lucia comes in her human form, because of having feelings for both her human form and her mermaid form. Kaito eventually realizes that the two are one, giving Kaito the ability to love Lucia no matter what form she is in. Dōmoto is derived from KinKi Kids Pink Hanamori likes.
Nikora is the virtual manager of the "petit-hotel" Pearl Piari (プチ ホテル パール ピアリ puchi-hoteru pāru piari?) on land, where Lucia, Hanon, and Rina work (in the manga, she is the owner of a bath house called Pearl Waters). A purple mermaid, she poses as Lucia's older sister in order to inform her of her mission. She has a crush on Maki, the owner of a bar. In the last chapter of the manga, it is discovered that she is seven years older than Lucia.
Hippo is Luchia's blue penguin sidekick. Luchia's guardian who serves as her guide. Hippo accompanies Luchia in her search for her pink pearl, and is among those who voice disapproval of her relationship with Kaito. He is also polite, always putting -san, (-さん) after every name, even when angry. In the anime, he is shown as Luchia's pet penguin. Later on, he is able to transform into a very cute human boy, as well as a creature called a Hippocampus. In his human form, Hippo falls in love with a Dark Lover, Yuri. Hippo transforms into a Hippocampus using a key he got while trying to save Taro from Sara. His real form as "Hippocampus" resembles a unicorn.