@Mintzu I think it's like the demon possession by Satan in Ao no Exorcist. The first assassination attempt was successful but now his body has been inhabited by some otherworldly being whose power is basically wrecking the body so they had to sequester some of their power outside the body so it wouldn't fall apart.
i don’t think they are siblings especially when he said “she wants to protect her little brother” implying not to him so he could be just possessing the body. i am liking the drama
they're not real siblings, Nguyet is the daughter of her mom and the mother's assistant. But they have connection with each other long long ago (2500 years ago lol)
I love how clever she is, doing her best to manufacture these "bonding" moments. Then again, he's a little manipulator also... seeing these two trying to manipulate each other is hilarious!