This is, in my opinion, by far the best looking doujinshi featuring Cala in VIPER-RSR. It's called Beast Pox, but the creator also has a bunch of other images he created. The artist's name is Oni no E, he's done some other work that is also really good, but since this is about VIPER doujinshi I'll just share the RSR stuff he's done unless someone asks for his other work. I'll attach some of the pages then put up the entire thing in RAR format.