Hmm. Cousins would work pretty well, but Rei isn't really the type to get close to male family members (Thanks dad), so maybe they've met a few times...and he seemed alright to her? Probably did come by the shrine, even, but she probably never really took the time to get to know him beyond the surface.

But then he disappeared, and that wasn't entirely something she'd expected. Cue him turning back up and her being surprised, and actually happy to see him (and in a better position now to actually want to get to know him). How's that sound?