I'll try to make this review as spoiler-free as possible. It's a great manga for those who enjoy erotica and fantasy, with a pinch of action. The reason I had given a 9 out of 10 for the story was because of not the ending itself but how it ended and left things. There were many loose ends left, and a lot left to imagination, and a sequel would be of help. Part of the story during the middle started distancing itself from the main two, and you'd rarely see them.
Overall, it's an interesting story and I would recommend it for supernatural/smut/yaoi readers. Note that the sex for the two main characters at the start isn't very love-filled until later on in the story. Yeah that's about it.