Takamine may not be the only one with a supernatural ability, this new girl may have one that can maybe either neutralize, compete, or identical to it, this is the only way I can see where she could be any kind of competition, threat, rival, etc to her. It may also be why she flashed him.
I know new girl wont get anywhere but god damn it, she's already infinitely more likable than Takamine. Do the right thing author, for the good of mankind
Treat your love interest like garbage the whole story (even threatening him with a false rape accusation that has yet to be brought up again) but then feel threatened when a new girl comes along and treats him like a man lmaoooooooooo I hope Eri crushes her gem in the end.