They were all created by Gaito. They were ordered to capture the mermaid princesses, failing every time. The only mermaids that were captured was Coco and Yuri and Gaito captured Noel when she protected Rina.
They also compete with each other for their master's affections. The closest being Maria. At the end of season 1, they gave up their physical form to assist Gaito in fighting the mermaids. They are later seen in their original form in the throne room with Gaito and Sara, when the castle sinks to the bottom of the sea/ocean. At the end of season 2, they are seen with the whole cast of both seasons, singing. It is unknown if the whole thing was just a play or not.
- Maria - Maria is the one closest to Gaito in terms of love. She is also very cruel at times, and sometimes seems to see Gaito more as a boy-toy than a love prospect. She has the power to make and/or manipulate ice and snow.
- Yuri- The youngest-looking of the four. She has the ability to control people and objects, especially with the use of her music and, if any, a nearby piano. Although Yūri is loyal to Gaito, his continued treatment of her as a child leads her to a star-crossed relationship with Hippo, i.e. his human form. She is created from a fish
- Izuru - 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.
- Eriru - Eriru is the one with the multiple personality disorder. At one phase, she is cute, beady-eyed, and acting as if she were antsy (spinning around and never saying any normal speech). In another phase she can speak correctly and is more observant of her surroundings. In her third phase, when threatened (or when she spins around), she becomes scary, her eyes glow red, and she changes her voice accordingly.