User blog comment:B214/Volume 23 discussion blog/@comment-28087053-20170318185110/@comment-10330822-20170319022517

Yeah, but remember that Issei explained he "had" to think of her that way because she was "too pure". He even had to "correct" himself when his mind started to take him places. So to be honest, their relationship was never platonic, Issei was just trying to force it to be, but Asia's always been after him. Likewise, Asia isn't married.

Also, Rias's thoughts like that didn't last at all. Hell, it barely lasted a volume. She was already falling for him before the Riser Rating Game, so its obvious she didn't think of him as a brother "that much".