I think rei will get mad at her if she harm his best friend so I don't think she will use his best friend and I think he will most likely staying by her side for now and will eventually find a way to free himself from the bindings to his soul.
When the hunters are hunted, or haunted more like.
And our suspicious were correct, the guy is a complete simp, he can just fly away now doesn't he?
But of course not, he wanted to see his captor in swimsuit, understandable.