Book Idea - spin off to Chronicles series

One of these days I need to decide on an abbreviation for "Chronicles of M" so I don't have to continue typing it out. Who knows, maybe it'll turn into an established hashtag that way.  :P

Anyhoo, I've been thinking about writing a solo book centered around Mai (semi-important character for books 2 and 3) where it shows her life as a Japanese demon hunter and how she came to possess Oni, her Katana that may or may not be sentient (no spoilers here, suckers). If I do this, I'll probably spend a good chunk of time prior to writing it sitting around reading japanese folklore and watching their insane action movies. Not to steal ideas, mind you, but to get a better feel for the presentation. So, if you have any suggestions or fun ideas centered around Japanese demons, spirits or anything really, let me know. I love researching this kind of stuff!