The most common interpretation is that Kasen is an oni posing as a hermit for some reason.
It makes sense, but it seems too easy. I'm hoping there's more to it than that.
She is also hinted to be one of the four deva's of the mountain along with suika and yuugi.
edit: I posted this comment before reading weatherflonium's explanation. That's a better explanation than mine.
last edited at Apr 29, 2015 4:04AM