Catching up, but wanted to comment anyways: Diina seems very likely to be Venus, or at least has the demons believing she is Venus. I definitely wouldn't call her opposed to Lufasu from what we the readers are shown, but she definitely has her own thing going on. If she was actually on the demons side, she would want the city and Merak to be destroyed, but this chapter clearly shows her "3rd party" status. My guess is she is actually Alovenus, hence her pretending to be ***Venus. Authors of these sorts of stories like lining up stuff like that.