Japanese erotic games do feature hardcore sex scenes, but there is an "adventure" part during which players interact with fully clothed characters. While there are exceptions, those clothes are often dorky. Very, very dorky.
A recent thread on 2ch, Japan's largest bulletin board, asked why erotic game characters wear such unfashionable threads.
"It's because people like you are designing them," quipped one 2ch user. Another pointed out that creating fashionable outfits was tricky.
"Look at your own clothes, and then you'll know," chimed in another. "There's no way geeks can make cute outfits for women."
It was even pointed out that the guys' outfits were not very cool, either.
Part of the issue is that if the game developers aren't good at picking out fashion trends, the in-game characters look dorky when the game's finished. Then, there are those players who think it really doesn't matter, because the characters will take off their outfits anyway, while others would argue that these outfits are part of the fantasy. Still, some find the uncool clothing off-putting.
Probably the safest bet, wrote one 2ch user, was to put the characters, who are usually students with student pocketbooks anyway, in simple Uniqlo style outfits. Those can then be coordinated with pricey outerwear or shoes. That sounds more like shopping advice than concerns over nerdy ero game fashion.