Other Characters of Mermaid Melody
These characters are critical to the ongoing of the series. Some show up before/after or more often than the other, but they are all either helpful or hurtful components that allowed the Mermaid Princesses to mature.
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, and has yet to realize that this mermaid is Lucia. 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 Panthalassa and is the younger twin brother of Gaito. 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.
Lucia's guardian who serves as her guide. Hippo accompanies Lucia 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 -さん, -san after every name, even when angry. In the anime, he is shown as Lucia'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. In many anime shows Lucia and the other 5 mermaid princess try to get them meet, even for just a short time. Hippo transforms into a Hippocampus using a key he got while trying to save Taro-chan from Sara.
Nikora is the virtual manager of the "petit-hotel" Pearl Piari on land, where Lucia, Hanon, and Rina work. A purple mermaid, she poses as Lucia's older sister in order to inform her of her mission. In the last chapter of the manga, it is discovered that she is seven years older than Lucia.
Madame Taki is the owner of the Pearl Piari. A fairly major character in the anime who is a fortune teller and friend to the mermaid princesses. Everyone thinks her predictions are wrong, never saying yes when she asks if they want one. Sometimes though, they are right, leaving them astounded. It was also shown in Episode 13 that she can turn into a clam, possibly so she can swim under water and for protection.
Tarō is Lucia's music teacher and Hanon's love interest. He had met a mermaid in the past (Sara), and made a piano piece for her, not knowing what happened to her after their last meeting.
Aqua Regina is the ocean goddess who gives the Mermaid Princesses new songs and upgrades for their gear. However, this is all that she can do alone after expending a great deal of energy thousands of years ago. She is needed to ultimately stop the sea monsters, and the seven pearls have to be gathered to summon her; Gaito/Gakuto seeks to summon her as well, so that he can use her to destroy the world. Aqua Regina later gives bands to the mermaids to upgrade their singing power; as in many magical girl series, this is signified by adding frills and accessories to their dresses. She also upgrades their microphones in the end of season one, before she is finally summoned. At the end of the manga, Aqua Regina reveals that Lucia is to be her successor.
Mikaru is the girl who finds Kaito after he had lost his memories. She's a rich, yet desperately lonely girl who has lost all hope; she falls "in love" with Kaito to the point that, in Lucia's perspective, he has forgotten his mermaid love completely, and is desperate that he return her feelings. Mikaru also seems to be a sickly girl, collapsing to the floor every time Mikaru appears somewhere else or when Kaito is near Lucia (in order to keep Kaito to herself). In the manga, when Kaito states that he loves only Lucia and could never love Michal the way that she "loves him", Mikaru takes off her clothes and offers herself to him in desperation of keeping him; Kaito turns away from her and leaves. This is a large trigger for her collapses and allows Mikeru to take control of her. In the end, Mikaru is reborn and given to her brother to raise her from scratch.
Rihito is an orchestra conductor and Michal's older brother. After initially seeing Kaito and Lucia at the airport, he becomes a "bridge" for the two. He observes Kaito's progress in regaining his memories (despite his sister being around) while he checks on Lucia and comforts her as she copes with the loss of her emotional bond. Rihito tries hard to get Michal to realize that she could never be with Kaito even though she doesn't want to hear it. In the anime, when Kaito leaves after telling Michal that he loves Lucia, Rihito restrains Michal from going after Kaito. When Michal is reborn, he promises that he will care for her and raise her again. It is later revealed that both he and Michal are part of the same race as Kaito, leaving Rihito to believe that that is the true reason why Michal is attracted to Kaito.
Masahiro is a flirtatious boy who has a crush on Rina. He wears glasses, rides a motorcycle and does some amateur boxing. It is later revealed that he comes from a family running a boxing gym. At the end of the manga and the anime, Masahiro is Rina's boyfriend.
Nagisa is a young boy who has a crush on Hanon. After retrieving some sheet music for Hanon, he has been wooing her ever since. Unfortunately for him, the sheet music is of the tune Tarō Mitsuki dedicated to Hanon, which only reminds her of her fixation on the much more refined and older man. Still, his resilience is to be admired, and she eventually treats him better. In the manga, he says that he is two years younger than Hanon. In the end, Hanon falls in love with Nagisa and they have a relationship at the end of the manga.