Mimi and Sheshe are thought to be lovers and in some cases this is true, in the manga, they are. Mimi is the younger sister of Sheshe. Mimi is a mercenary of Gaito, and not in love with Gaito like the Dark Lovers. Mimi is more of a follower of Sheshe, and in their song, she sings the chorus. Their song causes pain to mermaids.
They are the first villains to sing evil songs as an offensive attack against the Mermaid Princesses. Throughout the series they appear to act more than just sisters, more like a teasing rather than a normal relationship. They used Coco and Noel 's pearls to strengthen the power of their songs, and to make them immune to the Mermaids' attacks in Episode Sheshe is the elder sister of the Black Beauty Sisters.
Lucia, Hanon, and Rina, on a quest to save Karen in a coral reef, are lured into a trap set by the Black Beauty Sisters. Aqua Regina gives the trio a new song thanks to Kaito. Karen forgives Rina about Noel in the end. The mermaid princesses had searched for Karen all moring in the sea but couldn't find her anywhere.