She is Koo Jun Pyo's elder sister. As the elder child, it fell upon Koo Jun Hui to raise Jun Pyo as their parents were largely absent. She did so through aggressiveness, which included hitting and kicking him. She is the only person who can control him, as he listens to her. She also defies their mother by openly supporting his relationship with Jan Di, and they become close friends.
(Source: Wikipedia)
