Ceres was a tennyo (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. (myanimelist.net)