Nikora

Nikora is a mermaid [centered around the color purple] from Lucia's kingdom in the North Pacific Ocean. On land, she acts as Lucia's Onee-chan [older sister] although she is actually something more of a caretaker/nanny. Because of this, you can usually find Nikora scolding, yelling, or reminding Lucia. We can assume Nikora has a fairly high position in the society of the mermaids because she looks after the princess. In the manga, Nikora runs Pearl Baths, a public bathhouse. In the anime howevever, she manages the Pearl Piari, a miniture hotel on a beach front [Also called "Pearl Waters"] Towards Episode 40 and on, we can see that Nikora has a relationship with Maki-san, the owner of the beach house/ bar.

Madame Taki

Madame Taki is known as a fortune teller who's predictions never come true. You can usually find her in the anime series with a crystal ball. Although Madame Taki comes from the mermaid world, she herself is not a mermaid. Like Nikora, she must also have a relatively high status or rank to be able to watch over the Mermaid Princess Lucia. Madame Taki owns the Pearl Piari on land but isn't usually seen.

Hippo

Hippo is, indeed, a very unfortunate name bestowed upon a penguin, who has no relations what so ever with actual hippos. However, later on, the true meaning of his name is revealed. In the mermaid world, Hippo acts as Lucia's guardian. On land however, Hippo is Lucia's pet penguin, although he is treated more like a servant for the most part. I would like to point out that the characters in Mermaid Melody are extremely dense, as penguins are not kept as pets. For some unknown reason, all the minor characters act as if seeing a penguin out for a walk was a normal thing. But otherwise, Hippo is very polite, using -san to everyone even when he is mad. He is also extremely unlucky, as in nearly every episode he is punched in the face by Lucia, smacked by a towel one way or another, assaulted my other penguins [like the aquarium], or thrown across the room by Kaito. For the most part, Hippo has three forms, two of them being dressed in sailor outfits. Hippo's first form is his penguin form, which is the one you most often see him in. Generally you see him in a sailor outfit in this form, but a maids outfit [apron] is also seen, usually while he is working in the kitchen. His secondary form appears every so often, which is Hippo as a human boy. Other characters have called him "an extremely cute little boy" but Hippo does not appear to like this form very much. He remarks in the anime, "I turned human because I stayed on land too long!" Hippo's third and final form is that of a hippocampus. A hippocampus is actually a mythological creature from Greece. They are the most prized kinds of horses because they have the tail of a mermaid but the front hooves and front body of a horse. Hippo is seen in this form sometime around Episode 30 while protecting Lucia, Hanon, and Rina from the Dark Lovers & Black Beauty Sisters. However, it is known that Hippo could not transform into his final form until he somehow aquired the key to Gaito's castle, which then, fully unlocked his powers. It is also very well known that Hippo likes the water demon, Yuuri, and has an entire episode dedicated to their relationship [Episode 42]. Later on, Gaito uses his remaining power to let Yuuri have one night, and one night only, with Hippo to say good-bye.

Aqua Regina

Aqua Regina is the "Goddess of the Ocean World". She used to be a very powerful being, but now she is only a ghostly figure. This is becuase thousands of years ago she used her powers to seal the Panthalassa clan in the deep ocean. However, she depleted her powers when she did this. She can only be revived if all the Mermaid Princesses' seven pearls are combined. Aqua Regina is the only person who can stop Gaito and his clan. Until then, her ghostly spirit stays at the North Pacific Ocean, the last kingdom left from Gaito's attacks, to protect it.

Amagi Michal

Michal is a shy, lonely, sickly girl that appears in the Pure season. She lives with her older brother, Rihito, who is a famous orchestra conductor. However, she believes she is a burden to him and that he also hates her for it. Because she is always very sick and constantly moving, Michal never has time to make friends, and therefore has poor social skills. She was generally content with this unhappy life until one day, fate cruely let her taste happiness. Michal was in Hawaii for treatment when she stumbled upon a boy who had washed up on the Hawaiin shores. This boy was Kaito, but his accident caused him to have selective amnesia. By cruel chance, the only things that Kaito forgets is Lucia, the mermaid Lucia, the realization that Lucia is a mermaid, Hanon, and Rina. However, Michal didn't know that, and she was extremely happy with Kaito. She had to return Kaito to Japan, but in doing so, she also moved there. However, she decided that she needed to nurse Kaito back

Amagi Rihito

Rihito is Michal's brother. He is an orchestra who travels the world. Rihoto takes care of his sister by himself becuase his parents died a long time ago. When his younger sister falls in love with Kaito, he tries very hard to push Kaito and Michal apart becuase he knows that Kaito will remember Lucia and Michal will get hurt. This causes the siblings to grow apart, and Rihito developes frustration becuase his sister think thats she is a burden for him when he really does love her.