|Black Beauty Sisters|
|Members: Sheshe, Mimi|
|Relative Groups: Dark Lovers, Mikeru's Servants|
|Objections: Catch the Mermaid Princesses (former)|
The Black Beauty Sisters (ブラック・ビューティー・シスターズ Burakku Byūtī Shisutāzu) are two sisters, Sheshe and Mimi, they worked once for Gaito, for Mikeru. They are the first villains to sing evil songs as an offensive attack against the Mermaid Princesses. They have two songs called Kuro no Kyōsōkyoku and Yami no Baroque.
Throughout the series they appear to act more than just sisters, more like a teasing rather than a normal relationship. They were seen using Coco and Noel's pearls which makes their songs more powerful
Sheshe is the elder sister of the Black Beauty Sisters. She has long hair tied in a ponytail. She is a mercenary of Gaito, not in love with him like the Dark Lovers, but only willing to cooperate with him for personal gain.
The Black Beauty Sisters are the most powerful servants of Gaito, with a singing voice so strong that the mermaids can barely stand to listen to it.
She is more powerful than Mimi, because she has demonstrated all the powers that Mimi has and more powers that she hasn't demonstrated. She is also the one that does all the thinking instead of the work. The reason the Black Beauty Sisters must align with Gaito is because they, like the Dark Lovers, are also transformed by Gaito's spell. Sheshe's true form is that of a demon angler-fish.
MimiMimi is the younger sister of the Black Beauty Sisters. 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. She is the sister that does all the work instead of the thinking and takes orders from Sheshe. Like her sister, Mimi is also transformed by Gaito's spell, and her true form is a blue demon angler-fish. In the anime she becomes friends with the Mermaid Princesses, and cries when she finds out her friends are the Mermaid Princesses.
- Many fans call the first song of Sheshe and Mimi Voice in the Dark instead of Concert of Darkness, because that is the first line of their song. However, the real name of the song is in fact, Concert of Darkness.