I think I've seen Mamizou's outfit before, sometime when I was young, but I have no idea what it is.
Looks like something traditional from Hokkaido(?) (Ainu clothing??? No..., it can't be. Can it?)
Took a little hunting, only to loop back here, as it were. The hat/cape is a mino boushi ("straw raincoat hat"), used in the Tohoku & Hokuriku regions. (I'll add that tag once I post this.) The boots are fukagutsu ("deep shoes"), straw snow boots. I found one example that was specifically attributed to Fukui prefecture, which is a bit under halfway up the eastern coast of Honshu, but I imagine varieties are worn all over the northern areas of Japan.
The full outfit makes me think of something the late Mizuki Shigeru might have drawn in one of his stories.
I saw these go up this morning, but had to rush into within and didn't get a chance to post.
This picture gives me a real East Meets West feel, especially with Ran (the old youkai shikigami) being dressed in modern winter wear, while the recent arrival from the outside world (in the present day) wears the very old style gear.