Just for the new confused readers out there...
This is NOT incest. Not even close. Though they're taking a damn long time playing that part.
There are mental health themes. Its not a magical story, and is set in 19th century Europe. In the early chapters, quite soon after being taken in, the female lead starts showing hallucinatory symptoms characteristic of schizophrenia. The background for this is delved into as the story progresses.
It's hard to stick through the tense atmosphere and red herrings the author puts in the beginning and the pretend incest when the story isn't completely translated. That's ok. I would just humbly suggest to shelve it until it's done or close, because this definitely tells a different, interesting type of story.