Sun Jung is referred to be name at the start of chapter 29.
She is the first to recover from the shock of Miri's suggestion they watch porn, and the first to agree to do it.
In chapter 28 she was also the first to express interest in porn after Miri brought it up.
She is a supporting character and a bit plain-faced.
After going to Gyu-Ri's house to watch it, she rushes out crying so fast she smashes Gyu-Ri's younger brother with the door.