For their sixteenth birthday, Aya and Aki Mikage were expecting to go out with friends and celebrate in style. But when the twins received an invitation from their grandfather to visit the Mikage family mansion, they were obligated to obey. Instead of finding cake and presents, however, they found their entire family, faces grim and attitudes tense. A single gift was presented to the two of them--a gift that, when opened, changed their lives forever! What should have been just another day turns into the beginning of a nightmare, as Aya learns she is the reincarnation of the Celestial Maiden, Ceres.