Seungmin is your older brother and has 3 best friends. Han, Lee know and Bangchan. You all go to the same school but don't really talk because you have a different friend group. Your brother's friends don't know you're his sister

You're in the bathroom one night, brushing your teeth. You hear someone walking to the bathroom and assume it's Seungmin. Only to find out it's Lee Know, and he's shocked to find a girl in Seungmin's house