Siren

Siren is a friend of Hummy, also born in Major land. Last year she sung the Major Land's Melody of Happiness. But this year Aphrodite chose Hummy to sing it instead of her. She then felt betrayed and went to Minor Land to ask Mephisto if she could be his servent. Besides being a cat like Hummy she also has a human form. Her human ego is named Ellen and her cure ego is Cure Muse (キュアミューズ).

Betrayal
Siren feeling betrayed by Aphrodite for choosing Hummy to sing the Melody of Happiness goes to Mephisto of Minor Land pledging her loyalty. On the day that Hummy was due to debut as the new singer of the "Melody of Happiness" Mephisto attacks stealing the Legendary Score and rewriting the notes to create the "Melody of Sorrow". Calling forth Siren to sing the new melody, Aphrodite being shocked over her betrayal, she begins to sing causing the crowd to start crying and feeling sad. Aphrodite stops the song and spreads the notes to a land where warriors are born. Mephisto sends Siren and the Trio of Minor after them.

First Encounter with Pretty Cures
Siren, in the guise of Ellen, meets Hibiki first and is eager to take the G Clef sealed in her heart. Hibiki runs outside only to see Kanade holding a record the two girls used to listen to together. Siren sees Kanade has the same G Clef as Hibiki and orders the Trio of Minor to take Kanade's while she takes Hibiki's. Before they even reached the G Clefs, the emblems suddenly shone, throwing back Siren and Trio the Minor. As she regains her footing, she sees one of the notes from the Legendary Score on the record and quickly transforms it into a Negatone which calls forth a monster to attack the city and spread the sorrow. Hibiki and Kanade were angered by this, and the emblems in their hearts came out and transformed into Cure Modules, which are items that allow the two girls to transform into Pretty Cure.

Betrayed Again
During episode 10, Siren was injured and is about to get hit by a car until Ouji saved her. During in his presence, she cannot reveal her true nature to him but somewhat developed a bond between humans. The next day, Siren hesitates due to Ouji's presence. And one of her stooges, Bassdrum, transforms the gifts Hibiki and Kanade received into Negatones which they defeat. Afterwards, Bassdrum denounces Siren as their leader. Later, Mephisto declares Bassdrum as the new leader due to Siren's sudden change.

Cure Muse
Even though it's not confirmed yet and it may not be true, many think that Cure Muse is Siren's cure form, first appearing in Episode 11. She wears a mask with a heart-shaped jewel on it, and is shown with a purple Fairy Tone called Dodory on her shoulder and a Cure Module on her chest. She actually resumes in this form to help Melody and Rhythm during their battles against a Negatone. She also doesn't seem to speak in this form, as her Fairy Tone partner, Dodory, does all the talking and denies to be their partner.

Abilities
Not much is known about her powers, but she is shown to be able to create a rainbow piano by clapping her hands together and spreading the keys out, and then shooting the keys at an enemy, which traps them long enough for it to be purified.

Relationships

 * Hummy - Siren was a friend of Hummy but after Aphrodite asked Hummy to sing the song instead of her. Siren felt betrayed and became Mephisto's right hand. She tends to yell at Hummy as to try to argue but Hummy is just so optimistic it doesn't really matter.

Ethymology

 * Siren is a reference to Greek myth specifically the Odyssey where a group of beautiful witches called the "Sirens" would sing to lure poor sailors to their deaths by making them crash their boat onto the rocky shores of their island.

Trivia

 * Siren is the only mascot-like character to be a villain. She is also the second mascot-like character to become a Pretty Cure, the other being Milk.
 * Siren also has a human form like the mascots of Yes! Pretty Cure 5, Yes! Pretty Cure 5 GoGo! and Coupe of Heartcatch Pretty Cure. She first introduces herself in this form to Hibiki as Ellen.
 * Although her main form is Ellen, Siren also seems to be able to disguise herself as any human as she does this to try to fool the Cures. This is somewhat like what Poisony from Futari wa Pretty Cure does to Nagisa and Hanoka in that series.
 * Siren is the only mascot character besides Hummy to be a cat.
 * Siren has used Ellen and to decrease Hibiki's and Kanade's Harmony Power by disguising herself as a transfer student named Houjou Sakura.
 * Siren is the second villain who is been rejected by a villainous group due to her weakness, the other being Higashi Setsuna of Fresh Pretty Cure!.
 * It can however, be speculated that she can be the Fourth Cure revealed in the latest scan in Nakayoshi, but this was not proven. But in Episode 12, it was shown that both Siren and Cure Muse were the same person after Bassdrum addressed her in her real name.