Feel free to post your interpretation below!
For me the heroin got abducted by an alchemist who seeks eternal life, much like the plot from Kai Meyer's
Die Alchemistin. She is not there to be sacrificed, but rather to serve as a parent for the children who are kept in the building.
But the heroin awakes to early and tries to escape, and - in the case of my first run - she goes back to being a parent.
In my opinion the key of this fiction is a special ability of the children that are being kept. The alchemist must have found a way to use their youth as a philosopher's stone. It's unclear whether he could use any given child for his purpose or if he chose some who had some powers. My interpretation is that he just kidnapped random kids
