correct me if I'm wrong, but wasn't it Mei that initiated "first contact towards" (kissed) Yuzu? [ OK, OK, I'll go reread the previous chapters to confirm, but in the meantime... humor me on this conspiracy theory] so what if this mystery person was the reason Mei kissed Yuzu in the first place?
OK, now I'll go reread the current chapters so I can clean up this post in case I am waaaaay wrong.