Why everybody wear them black latex drawers?

While this is a rather funny thread in a more serious answer they do wear more on occasion. Feng in the orange dress thing has orange underwear while the Spirit in the school girl outfit has black and surprisingly Hag has red in her dress and all the survivor models themselves have an underwear version with Yui having a topless version as well. I've also heard Zarina has a topless model but that one I can't confirm.

For those obviously curious I had to taint to my google for these. No Yui one though, that you'll have to get on your own.