It may be a 'compatibility detector', sensing who is the most fitting partner at the time. Just a guess though.
If it is, it's probably a more advanced form than Koyuki's, which either shows a rejection or the ok sign.
It definitely could be, but Koyuki has already been given the 'naivete' and 'shy' traits, so I'm reasonably sure she never intended it as such. The new girl seems less likely for those traits.
ditto, you expressed that idea more clearly then I did haha