New character to shake things up, huh? Well since the premise of the story is basically a miscommunication and there's been clear romantic progression despite the current cast as it is, the story was on course to be 'over', so I'm actually fine with this little shake up. The backstory between her and the guy is pretty clear, her introduction didn't induce any misunderstandings at a point where we at the 'finish line' (I'm looking at you Masamune-kun), and we're going to get some opportunities to deepen the relationship by her standing up for him (or vice-versa if new chick knows how to manipulate people around her rather than relying on physical strength). Just feels like a good use of introducing a new character IMHO.