Mimi is an antagonist in the Mermaid Melody series. She and her older sister, Sheshe, together form a pair known as the Black Beauty Sisters. Mimi is the younger of the two and is distinguished by her light blue hair, while Sheshe has red hair. They are hired by the villain Gaito after his earlier minions, the Dark Lovers, fail repeatedly in capturing the mermaid princesses.

Mimi is a mercenary who works for Gaito, but unlike the Dark Lovers, she does not harbor romantic feelings for him. She is instead deeply devoted to her sister and largely follows Sheshe's lead. In their musical performances, Mimi typically sings the chorus part. Her personality is less hot‑tempered than Sheshe’s; she is more inclined to either shrug off troubles or complain about minor annoyances, while Sheshe bottles up her anger. Together, they are fiercely loyal to each other, with Sheshe looking out for Mimi and Mimi adoring and idolizing her sister in return.

As part of the Black Beauty Sisters, Mimi’s primary role in the story is as an obstacle for the mermaid princesses. She and Sheshe use their singing abilities to attack their opponents. Their signature songs, Kuro no Kyousoukyo and Yami no Baroque, have the power to induce severe headaches in mermaids and leave them feeling defenseless. In the second season, Pure, they receive additional power from the angel Michel, which allows them to generate powerful whirlwinds.

Mimi appears in both the first season and the sequel season, Mermaid Melody Pichi Pichi Pitch Pure, as a supporting antagonist. She also appears in the sequel manga, Mermaid Melody Pichi Pichi Pitch Aqua, though her role in that story is minor and not elaborated upon. Throughout the series, she remains a consistent antagonist, showing no significant change in alignment or motivation beyond her loyalty to her sister and her tasks for Gaito.