Hey there,I made a quick sketch as a sort of inspiration for those who need it. I can't get the style right but I thought the demon could be drawn as a distorted version of noir girl.
As I see it the man comes across the tower and perhaps unconsciously hopes to find the princess he saw on the book he once read. So it could be interesting to show the contrast with reality and the man's interpretation.
It could be fun also to draw what the town people imagines when the man describes mademoiselle noir.