She is a C-Genomer who actually looks like a guy. She's very good at singing. Long before, she has a partner in singing, by the name Kei however her partner was killed so he pursued singing as a solo.

Ceres was a tennyo, a celestial maiden, who came down from the heavens to bathe in a stream. She hung her hagoromo (robe) on a tree nearby, which was her key to returning to the heavens. But the robe was stolen and the man who had stolen it forced her to become his wife, thus producing a family full of human and tennyo blood mixed. 
Now, in modern day time, Aya Mikage is a descendent of Ceres, and has quite an amount of tennyo blood. On her 16th birthday, she and her twin brother, Aki, are thrown a party. At the "party", Aya's grandpa plans to kill her, for she has tennyo powers unlike the rest of the family, and can actually become Ceres herself and destroy the Mikage family. Aya, however, can switch back, so this transformation happens quite frequently. 
With protector Yuuhi by her side, it is up to Aya to control Ceres and keep her from coming back, but her relationship with an ex-worker for her evil grandpa may be a distraction.

Aya and her twin brother Aki thought they were going to a celebration of their sixteenth birthday at their grandfather's home, but the funeral-like atmosphere tips them off that something's not right. Their "birthday present" turns out to be a mummified hand--the power of which forces an awakening within Aya, and painful wounds all over Aki's body! Grandfather Mikage announces that Aki will be heir to the Mikage fortune, and Aya must die! But Aya has allies in the athletic cook and martial artist Y&ucirc;hi, and the attractive, mysterious T&ocirc;ya. But can even two handsome and resourceful guys save Aya when it's her own power that's out of control?
 
(Source: Viz Media)
 
Notes: 
- Winner of the 43th Shogakukan Manga Award in the shoujo category.

Shuro Tsukasa