Camera Fiend: Mrs. Q, that filmed Aya and Aki's reunion and Yuuhi kissing Ceres to turn her back into Aya.
Chekhov's Gun: Aki's scars turned out to be significant: they were inflicted on his past incarnation by Ceres.
Reincarnation-Identifying Trait: Ceres identifies Aki as the reincarnation of the man that stole her robe by the scars Aki received on the first episode: those were inflicted by Ceres on Mikage.
Reincarnation Romance: Heavily implied that Aya and Aki are in inversion of this trope.
Ship Tease: Lots between Aya and Touya, including Aya thinking to herself that she fell in love with him.
Yuuhi kisses Ceres again to revert her back to Aya.