It can't. The only way it could cause Yaoi here is to reveal that they were both boys all along.
Well, it can't do it all of a sudden, but it might force them to become "male" in some way or another, either involving surgery, Yukari, Eirin, some miracle, or even all of them at once.
Well, it can't do it all of a sudden, but it might force them to become "male" in some way or another, either involving surgery, Yukari, Eirin, some miracle, or even all of them at once.