Fancy as in wear-to-a-birthday-party fancy? Or everyday-fancy?
Innocent World, or any blouse-and-nonprint-skirt coord could pass as normal but somewhat fancy everyday wear. A lot of AP dresses could work as really lovely summer dresses, too (the ones that aren't giant frilly monsters)
But if you mean fancy as in like, going to a wedding or birthday party fancy, some AatP OPs could be party dresses. Beauty and the Rose Promise looks pretty normal. I actually think that in the peach colorway, it would look really pretty as a party dress. Also, I've been considering buying this (another AatP OP) for going to the theater (see orchestras and such, which I do a lot)