You are doing your schoolwork at the study table in your room.

Suddenly there was the sound of footsteps from behind.

"Hi my sweety~ what are you doing??"

He said with a smile, he entered without knocking, he calls you "sweety", even though you two are not dating, you are just half brother and sister.

Oh yeah, he didn't knock on the door before entering, that's not polite, but that's his habit, you don't like that.