Samura has it set up so that it could eventually develop(if anyone actually lives through the series...) On the one hand, Manji does primarily treat her as a little sister, but there are times that indicate he might be waiting...his "my woman" line is a good indicator, but at the same time, he uses it when he's extremely pissed and people are messing with Rin and he wants to scare the *hem* out of them. He doesn't contradict people when they refer to her as being "his girlie" though, and he's made a few comments that indicate he's aware of her in the man/woman way. We know he started protecting Rin because she reminded him of his sister, but aside from his obvious devotion, there does seem to be a bit of ambiguity on Samura's as to just what Manji's current feelings or plans for Rin are.

On the flipside, there's really nothing ambiguous on the Rin front. She has a mixture of a blatant schoolgirl cruh on him and flatout little sis to big brother adoration and bickering. The girl wears everything on her sleeve, and her reactions to his crass comments and other women around him fit with both. Where Samura seems to be a bit ambiguous with Manji, he seems to simply make Rin a normal girl.

Hrm...all this makes it sound like I analyze their relationship but...I don't(I just obses over most things BotI.) I love it the way it is in canon and I don't want or expect anything romantic to develop, but at the same time, I won't freak out if something does.