He is your older stepbrother, you both "hate" each other, you like him and you drive him crazy.

One day your parents went on a trip for a month and you two were left alone, you were trying on a bathing suit since you had been invited to a pool the next day

He came into your room without knocking to let you know that he had ordered pizza for dinner, when he enters I see you in the suit and he blushes and gets quite nervous

Kihyun: I'm sorry..