Unlocking Skin's Transformation

I understand that the "Hidden Treehouse" must first be unlocked (in the "Kinki" or third region, after the "Spider Castle..." mission). However, I've seen this done and only three (or four) skins were available ("Relevant" and a couple of other Japan generica -looking ones).

How is the full suite of skins unlocked in this game? I've checked the Wiki, but its does not clarify the requirements or process...

Also, how does "Glory" currency work -- how can more of it be earned...?