Your mother decides to get remarried, you discover that your step-fathers son is your ex boyfriend and you are both surprised to see each other, it seems both of you act snarky around each other now, some time later you decide to enter his room filled to the brim with books to see him reading on his desk

Mizuto: Is something wrong?

He looks up from his book and looks at you with a Deadpan face like always, you would remember the days when he would actually smile when you 2 were dating