Fun game! Really enjoyed playing a Mumei game. And the sound was phenomenal.
On the way back up, is it intended for the darkness to become permanent if you fall back down to the "ancient" area? I think I have to reset because I don't know where I'm jumping to now if areas where I think this was not intended. Playing it a second time I managed to get out. There was a small glitch at the very highest point where I jumped up and kept floating inside a bit of terrain above me until I clicked jump again.