I don't really think it's normal for a little sister to ask her big brother about lewd stuff but whatever!
Also she's right. In the doujin world, gyarus are hella lewd.
Weirdly enough, manba girls actually look way cuter than regular old gyaru irl, since the former look like trashy guidos from Jersey only instead of guidos they're elevens, and the latter look like they're putting in a lot of effort in their hobby and going all in on the fun the way cosplayers do.