AYAKA A surfing student of Kaito's, upon the surfing shop owner's request. I swear, this girl is SUCH A BITCH! She thinks she can get any guy she wants just because she's pretty and "older". On top of that, when she sees how much Lucia likes Kaito, she comes up with a dirty plan. Hoping to sink Lucia's boat and breaks her heart at the same time, she gave Kaito two tickets to the "Mermaid's Eye" cruise event; and when Kaito and Lucia enter the cruiseship together, Ayaka pops out and claims to have a "date" with Kaito. Luckily, she got REJECTED by Kaito afterward! ^__^

SAKIYA KOUSUKE West Japan's champion surfer, and Kaito's surfing rival. They are not overly competitive though, which is a good thing ^^; Kousuke has a cheerful and laid-back personality, which attracted a good following of girls. He is a flirty guy as well, like Kaito. On the day of the national surfing contest (see episode 8), he ate the bento that Lucia made for Kaito, thinking that it was for him.

ISHIBASHI YUYA We meet Ishibashi-san in episode 10, when he stands beside a bus stop, trying to spot the perfect model that he can use in a model contest the next day. Obviously he is a make-up artist. He chose Lina because not only she is incredibly beautiful, but she reminds him of his ex-girlfriend. Lina later teaches him not to let the past conquer his life, and is rejected by her anyway when he is in love with Lina herself. The poor guy! Through him, we are able to learn more about Lina, so his role is quite significant.

AQUA REGINA The beautiful sea goddess who has control of the ocean world, and the only way to summon her physically is to gather all the mermaid pearls taken from each mermaid princess. Up until episode 13 she only showed up twice: in episode one when she gives Lucia her singing power, and in episode thirteen when she "inspires" Lucia and co. their new attack tune, as a projected image. So basically, for now cannot upgrade her power without the Aqua Regina's help. She is also the one who makes Lucia realize her responsibility as the head mermaid princess.