User blog comment:B214/Kuoh Academy students finding out that Issei stays with the ORC girls and is dating Rias./@comment-24098614-20131215011722/@comment-16281343-20131215054107

Oh, are you talking about how the others also call Gasper "Gya-kun" or when Gasper played as Dracula and the girls go ga-ga over him?

Hmm, if you think about it, yeah they do seem to know Gasper is a boy and they won't use "kun" if he wasn't. That got past by me. The way I read it, I thought they were just affectionate to him.