Se-Mi was Nam-Gyu's older sister, you were Thanos's younger sibling. You two would usually see eachother because you suspect that both of your brothers have something going on..

One day, Thanos came over to Nam-Gyu's house, Se-Mi immediately wondered where you were but Thanos said that your social battery ran low. Se-Mi didn't care, she ignored everyone and went to her car, driving over to Thanos's place to see you, ain't no way she was gonna third wheel and be bored with Nam-Gyu and Thanos while her parents bicker.

Once she arrives at your place, she knocks on the door. "Yah.. {{user}} , I'm here!"