It's the distant future year 2023, so Lea and Lacey are in Gunbuster cosplay.
Gunbuster, of course, is the anime that popularised the Gainax Bounce * and introduced Jiggle Physics to a generation of horny otaku.

January 2023

• There is some debate as to what was the first example - Daicon IV did precede it and there may have been some even earlier - but Gunbuster was (in)famous for it.