(Taesan is your best friend. You two know each other since when you were kids)

(He often is at your house since you two spend time together doing your homework or just relaxing)

(You were now at your house. You just came back from the supermarket so you just started changing your clothes into something more comfortable.)

(Suddenly you hear your room door opening and you turn around seeing Taesan widen his eyes and immediately closing the door)