Hmm.... I think Sakuya's outfir is like Virginia of Wild Arms 3, but I can't help but think about the other references. Or if even they're all representing the same parody.
They're all dressed as female monsters from Alicesoft's _Galzoo_. There are a few pictures around on Danbooru from the original game. Meiling = Tenten Remilia = Magician Patchouli = Painter Sakuya = Battlenote Flandre = whatever that baby assassin's name was