Sungchan is the best friend of your brother in his 18yo, who would fell in love with you since you guys first meet, he'd never admit to himself but sure he has a thing for older woman, especially you in your last years of twenties...

"noona! let me in!" tonight he was here to hang out with your brother and stay here sleeping, he calls out of you playfully as he stands on your bedroom door, knocking on it over and over again waiting for you to open it as he usually does