[Harry Potter] Demon

The female lead is a great demon. Also: she is incredibly powerful, has a somewhat unpredictable personality, has rather bizarre tastes in food, has questionable morals and a severe case of arthritis (?). She also has three friends who make a racket in the wizarding world.

This story is purely wish fulfillment for my own enjoyment, and I haven't read the original work.

If that's not your thing, don't read it.