Guiltythree
Theory: I think Cassie will be the bad guy. I think that Cassie knows Sunny's true name through one of her visions, but has not used it because she still considers him a friend. BUT, in the beginning, when see first saw 'the prophesy', she asked Sunny "to protect Nephis at all costs", which Sunny refused because he does not think he has the strength to do so. This makes Cassie to change expressions... What I think will happen is that there will come a time where Nephis will be in serious trouble, Sunny will be the only one able to help, but it will be so dangerous that he will either hesitate or outright refuse. Then, Cassie will call him by his true name and force him to help, essentially sacrificing Sunny's freedom for Nephis' life. And I think she has already foreseen this and that is the reason she is cold to Sunny. She considers him a friend, but at the same time has already decided that she will sacrifice him when the time comes.