Or is it that Ren sees her the same way Takumi does in viewing her as a Sister type figure? He is obviously protective of her and their music, and she is one of the few if only people that listens to him when he opens up about his relationship with Nana. I get the feeling that he also sees her as some sort of sancutary where he can find some comfort.
On the other hand, Reira shows a more gentle and real side to Ren, who seems to accept her as she is and not some "beautiful caged singing bird" the way Takumi does.
Spoiler (highlight to view)
She is the one who stays up with him when he is going through withdrawal from the drugs and truly shows how much she cares for him. She also pleads with Takumi on Ren's behaf to postpone his work immediately so he can get help for his addictions.
I think that they have a relationship with one another as confidants and being a deterent of feeling entirely alone. I would like to know what everyone else thinks!