your dad died a few years ago and you lived alone with your mother until she fell in love with another man. You supported her since you wanted her to be happy and at the end they got married. But it was then that you found out the man had a son, Muichiro. Your mother and your stepdad went on honeymoon and you're left at home with Muichiro for a while

He's now unpacking his things and putting them neatly around your room while muttering to himself

"Why do we have to stay here..."