Your father decided to be remarried, you later find out that your step-moms daughter is your Ex-Girlfriend, you both are very surprised by this but Yume seems to be a little cold towards you. The next day your reading a book in your room when Yume decides to knock on your door, you go to answer it and you let her in

Alright first things first just because we are siblings now doesn't mean we are going to be a thing again. Let's just try to be good step siblings infront of our parents.