Coco

Coco is the Mermaid Princess of the South Pacific Ocean and the Keeper of the Yellow Pearl. She is also friends with the Orange Mermaid Princess Sara. She is the second oldest after Sara. After Sara was left by Taro, Coco tried to be there for her, but she lost control of her pearl and caused great damage to both her and Coco's kingdoms.
Notes: In the manga, her kingdom was never harmed by Sara's pearl's power.
Later, Sara released Gaito from imprisonment and Coco was captured until she was rescued Lucia, Hippo, Hanon, Rina and Karen. Her capture makes her the first mermaid princess to become kidnapped by the sea monsters.

Coco has three forms: her mermaid, human, and Yellow Pearl Voice form.

Her mermaid form follows the trend of all the other Mermaid Princesses, with two pearl bracelets around her right wrist and tail.

In her human form, her long hair cuts shorter to her shoulders and become golden yellow in color. He eyes also become gold in color. She wears a necklace with her pearl inside it like the other Mermaid Princesses. She usually wears yellow clothing.

Lastly, there is her idol form, her Yellow Pearl Voice. Her costume is a short goldish yellow dress with a large light yellow stripe in the middle with yellow orange ruffles on the sides. The dress has a short knee-length yellow pleated skirt with an orange-yellow bow on the back. It also includes pale yellow high heel boots and light yellow gloves with cuffs.
Coco does not appear in a mermaid princess gown. Yellow Pearl Voice only has one outfit in the manga, and has received no power-ups.

In the anime, Coco shouts "Yellow Pearl Voice!" to transform. In the manga, Coco does not have a phrase to transform, she simply just transforms.Coco can sing to fend off enemies. Once joined with the other mermaid princesses, her voice's power increases. In the manga, she can even do so in her mermaid form and without her pearl.

In the Manga, Coco was captured when the story began. In chapter 14, when she is awoken, she decides to stay with Sara for unknown reasons. When she is awakened again in chapter 19, she realizes that the final battle is taking place. She then sings to help Sara remember that she loves Taro Mitsuki. Once, to battle Michel, she steals Hippo's key rod to fight him. (Chapter 29) She displays a fun-loving cheerful personality, playful and somewhat gentle, unlike her brash, arrogant anime counterpart. She also plays a slightly larger role than comic relief in the manga. However, in the manga, very much like the anime, Coco also likes to have fun, hang around boys, and occasionally displays a somewhat sexy side. She is a very devoted and loving friend.

Coco, like the manga, was captured at the very beginning of the series. She, however, was not awoken until the last few episodes of the season. She was crying in Lucia's arms for Sara, and therefore told them about her and Sara's kingdoms being destroyed. In a filler episode of season 2, she is seen hunting around for a shell that holds Sara's memories of the bad times, in fear that the memories would be released or taken into the wrong hands. This was not displayed in the manga. Also in the anime, she does not sing a solo. Coco is brash and arrogant in the anime, unlike her manga counterpart. She, though, as well as her manga counterpart, loves to have fun, hang around boys, and sometimes displays a somewhat sexy side.
Some viewers speculate that Coco admires Lady Bat, because when he winks at her, Coco blushes. It is unknown if this is true or not.

This is true, if you put this video on Youtube in minute 6:47, you'll see how Coco blushes: http://www.youtube.com/watch?v=28Jpp3WMtzE&feature=PlayList&p=EE96C836F7085791&playnext=1&playnext_from=PL&index=12
And in minute 8:10, Lady Bat almost bites Coco.