A villain (also known as antagonist, baddie or bad guy) is an "evil" character in any TV series, book or film. A villain usually is the antagonist, the character who tends to have a negative effect on other characters. A female villain is sometimes called a villainess (often to differentiate her from a male villain).
These are all the Villains of Mermaid Melody:
Gaito- The main villain of the first season and leader of the Dark Lovers.
Mikeru- The main villain of the second season and leader of Mikeru's Servants.
The first villains to be in the series are The Dark Lovers:
Yuri- She plays piano which makes humans become zombie-like.
Maria- She manipulates ice and snow, and can create large ice storms with a certain book.
Izuru- She can make water dragons and has the power to control waves and marine beasts.
Eriru- She has control over water, spins and becomes evil and more powerful than normal.
Black Beauty Sisters
There is also a group named Black Beauty Sisters:
(Sister) Sheshe- The older and the most powerful sister of the group.
(Sister) Mimi- The younger sister of the group.
There is a group named Mikeru's Servants:
Fuku- Mikeru's messenger.
Lady Bat- He can sing a song that can hypnotise people, and can make mermaids forget about their loves and the humans.
Lanhua- She can split herself into a dozen of smaller versions of herself to sing a song that makes people dance until they die.
Alala- She can control fire, sing a song that paralyzes people, and sing a song to make males fall in love with her.
Sara- The former Mermaid Princess of the Indian Ocean.
Mikaru- She formerly loved Kaito and kept him away from Lucia.