Ohmygod. Not only is this a beautiful picture, but I've been trying to imagine Tengu mountain as a civilization. But, even though I live in the mountains, I couldn't wrap my brain around it. Thank you.
Allow me to speak a little about what I believe might help you with trees.
Compare the trees in the lower right to the ones to the left of Momiji. The ones on the lower right would look like goo/jelly if the color scheme hadn't blended with the rest of the scenery. While the ones to the left of Momiji resemble trees indeed. My observation is that you rely a little too strongly on lines to make out a tree. As such, my suggestion is to try to make trees out of color alone (like traditional painters do), no lines. Give it a shot?
Otherwise, very panoramic, and the color is strongly sensual. The two elements, of scenery and character, blend together really well.
You draw one super awesome Momiji, and Aya doesn't look half-bad either. I really like the look of the buildings here; they blend really naturally into the mountain, giving the definite feeling that supernatural sorts of creatures live there.