> So this probably was what she was just wearing. But if she's not here, that would imply she went out somewhere, and where would she have gone after undressing...?
> Double-check Reimu's bed, to see if it looks recently disturbed, like she got into it and then had to get back out. (Or maybe she's buried herself into it.)
> ...
> Then look around to confirm that no one else is, in fact, present.
> Assuming we are indeed alone, change from our outfit into Reimu's, to see how well it fits (if it does at all).