Ayashi no Ceres is a anime/manga series by Watase Yuu, who also made Fushigi Yuugi, Alice 19th, and Imadoki. Mikage Aya and identical twin brother, Aki, go to celebrate their 16th birthday at their grandfather's mansion. Little do they know of the mystery and fate that awaits them. According to the lengend of the Tennyo (Heavenly Maiden), a fisherman stole the hagoromo (feathered robe) of a tennyo and she is unable to return to the heavens. She marries the fisherman and produces offspring. This tennyo's blood runs through the Mikage family. On the 16th birthday of every female descendant, she is tested to see whether she has the blood of the tennyo. Not only does Aya have tennyo blood, the original tennyo, Ceres, chose Aya to be the perfect body and reincarnated completely. Usually, descendants only have part tennyo blood within them. But Aya is the "original" and therefore has the most power. At the party, Aya's grandfather proves that Aya has tennyo blood by showing her a mummified hand, which she reacted strongly to. Aki, also reacted to it by having cuts all over his body. That proves that Aki is the reincarnation of Mikage, the fisherman who stole the hagoromo and husband of Ceres. Thereafter, Aya and Aki are separated as the story of the tennyo continues in Aya's time. If you're confused, maybe this link will help ^_~

This anime series is complete with 24 episodes. The manga series is 14 volumes but I don't have certain volumes.