Joo Won put on a total of seven kilograms (approximately 15.4 pounds) of muscle weight. He also went through three to four months of intensive training on performing stunts and action scenes, including car chases and handling motorcycles.
To show the urgency and confusion of Carter's situation, martial arts director Kwon Gwi Deok avoided the familiar production of a one-on-one fight and devised a way to show several characters intertwined in a dangerous situation at the same time.
Director Jung Byung Gil commented, "I tried to make the impossible happen in order to capture the [stunts] with real action instead of CG (computer graphics)."