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Karen is Mermaid Princess of the Antarctic Ocean, the keeper of the Purple Pearl.
She is the fourth Mermaid to appear in the series.
Like Hanon and Rina, Karen also escaped to the human world when Gaito attacked her kingdom. However, even though she is found out by the trio, she refuses to join them. Initially, she shows hatred for Rina. Why? Karen is the younger sister of Noelle, who was captured by Gaito. She heard how Rina was with Noel at that time, and was told that Rina left Noel behind. (In reality, Noel sacrificed herself to save Rina.) Karen, therefore, resolves to save Noel on her own.
Eventually, Karen saves the trio on various occasions, especially when the Black Beauty Sisters are introduced. Near the end of the first season, Karen sides with the trio as they are about to face the final battle against Gaito.
After the defeat of Gaito, Karen leaves to help rebuild her kingdom. She returns to the human world with Noel and Coco, and they end up becoming comic relief. Karen also returns for the battle against Michel.
At first, Karen is strict, and even a bit mean, but she starts to warm up to the trio and shows her playful side a bit. In Pure, karen is energetic and playful, unlike in the manga, Karen's personality was not fully revealed.
Karen has three different forms: Mermaid Karen, Human Karen, and her singer form, Purple Pearl Voice. Her image song is Aurora no Kaze ni Notte.