Hae-Gu, a proficient and merciless hitwoman, executes a man in front of his own daughter and takes the child under her wing. She decides to name her Mian, the word for "sorry" in Korean, and gives her one mission: "Kill me when you can." From that moment on, Mian decides that she will do this by choking Hae-Gu with feigned love and emotionally...