I'm totally agreeing with the things everyone said before about how sue has a tsuandere relationship with Quote, at least at the beginning.
Near the end, she really begins to care about him, as evident with the love letter, and her yelling at you to be careful after the final boss fight, and jumping off with you, which, as mentioned before, is very Romeo and Juliet esque
Anyway I really love sue and quote as a couple, but the feelings are obviously one way, unfortunately. I would imagine quote having more brotherly feelings towards sue, because he protects her (with the doctor, and igor etc).
Anyway that's just my two cents
bump