Arranged Marriage: Kagami leaves implied this applies to all marriages within the Mikage family, as they want to preserve the celestial blood as pure as possible.
Attempted Rape: Kagami tries to rape Aya in an attempt of bringing Ceres out.
Kissing Cousins: Played with. When Kagami assaults Aya, she's disgusted by the idea of having sex with her own cousin, to which Kagami's reaction is reminding Aya that marriages between cousins are legal.
Not What It Looks Like: When Yuuhi learns that Aya went to the hotel with Touya, he assumes they had sex, a misunderstanding that greatly annoys Aya.
Royal Inbreeding: Aya learns that her family is an example of this, with marriages between cousins happening with the intent of preserving the celestial blood.
