Last night I read this manga by Okama called Hanafuda. It's actually a pretty interesting love story with several plot twists in it, despite its genre.
(The story (spoilers!))
Anyway, it was good enough that it made me want to read up more on the folklore surrounding kitsune beyond what I already knew. Although kitsune just means "fox" in Japanese, in terms of these stories, they're supernatural creatures, and are sometimes called "fox spirits" or "demon fox" and they often have the ability to transform, along with other powers.
Wikipedia of course, was an obvious source. And the first two links in the external links section are particularly good. Especially the
second one, but both them have some PDF files of an old out-of-print book that can only be bought for hundreds of dollars (up to $1500) now. In other words, restricted library material, and not for normal people. Which I guess makes it fair use.