Definitely a permanent character, possibly for a thing. We'll see how learning humans goes.
As for backstory; well, her name's Respetiro, and she's a ghost cat.
The thing I may or may not have planned is a comic following her and one other major character, so no major info for now.
If the comic idea falls through, I'll be sure to post a proper ref and all the info pertaining to her, but for now she's a mystery.