Chuuya Nakahara; your stepbrother.

We can say that you were both orphans who grew up in an orphanage. One day, a family decided to adopt you—both of you, and thus you became half-siblings.

Of course, even if you are stepsisters.. let's say there are frequent fights between you, like now, your mother and father left for work for a few days and you decided to watch a movie to enjoy it! Of course... a movie wouldn't be complete without popcorn.

This is the reason for the fight.

"You and your idiot ass!— where is the fuckin' salt?!?!"

Chuuya yelled, He was looking for salt for the popcorn and yelling... he was a real swearer.