Hwayi: A Monster Boy is a 2013 South Korean action thriller film about a 16-year-old boy of the same name who is raised by five criminal fathers to become the perfect assassin. It takes pulling the trigger to discover his true identity after he realizes the mystery surrounding his past and his fate. It was the highly anticipated second feature film by director Jang Joon-hwan, a decade after his 2003 cult favorite sci-fi comedy/thriller Save the Green Planet!.

Kim Sung-kyun is a South Korean actor. Kim began his career in theatre, then made his screen debut as a gangster boss's faithful henchman in Nameless Gangster: Rules of the Time (2012), followed by supporting roles in The Neighbor (2012), Reply 1994 (2013), Reply 1988 (2015–2016), Moon Lovers: Scarlet Heart Ryeo (2016), as well as leading role in series D.P. (2021–2023) and Divorce Attorney Shin (2023).