It was somehow strange what Sergey did to Nina (if he did it). I'm not sure it really was characteristic to his character. But wasn't Nina supposed to lose the otome powers if it really did happen? Or do I remember wrong...

It was predictable Nagi would manipulate Nina even with the braindead corpse of Sergey. And Nina apparently fell for it. Ironic, considering what Sergey was planning to do.

The next ep indeed looks promising. A real bang, like Yukimura said.