I think the plot is leading up to where kay does get possessed by the goddess of darkness but then she realists that Aida is the reborn light goddess and the reason she doesn't have magic is cause she gave all her magic up.
I think the plot is leading up to where kay does get possessed by the goddess of darkness but then she realists that Aida is the reborn light goddess and the reason she doesn't have magic is cause she gave all her magic up.