Oh wow, it's Coffee for a change. What a twist!

Medieval low-fantasy AU where she's not a demon, but a fae, and kind of embodies the concept of knowledge.
She kind of has a crush on royal knight Tybalt Neravulpe, a mundane human. Once she put a glamour over pretty much the whole kingdom to overthrow the crown prince and seize his status and power... during that time, she showed herself to Tybalt and he gave her that piece of cloth she wears in her hair.
Her plan was foiled though so now he doesn't remember her at all.