I was searching through the board and found this old thread and I thought I have to say something to it.
I haven't read MM4 yet but in the first book were a few hints that they at least have known each other and that there were something between them, whatever it was.
true that. Rachel's the kind of girl that wouldn't go for a guy like Tobias without good reason. She is smart, pretty, and most of all, ruthless. Why would she want a wimp like him?
Ruthless? I don't think so. The Rachel in the first book wasn't ruthless. She was brave and she became ruthless during the war, but in the first book she was an almost normal girl. Very pretty, smart and brave.
I imagine Rachel as a protective person. Maybe they had classes together and she was nice to him. Rachel is not the kind of person who don't talk to someone just because the others don't like this person. Maybe she talked to him in class and she realized that he's nice and maybe she thought she was cute.
And Tobias? Well, Rachel was described as very pretty and self-confident and he wasn't. Maybe had a crush on her before the war started. And when he realized that this pretty girl was so much more than just good looking he fell in love with her.