In January 2013, Kim starred in military musical "The Promise". It was co-produced by the Ministry of National Defense and Korea Musical Theatre Association, to commemorate the 60th anniversary of the signing of the armistice. It ran from January 9 to 20 at the National Theater of Korea, with a cast composed of actors Ji Hyun-woo and Jung Tae-woo, as well as singers Leeteuk of Super Junior, Yoon Hak of Supernova, and Lee Hyun of 8Eight. The musical centered around a group of soldiers who keep a promise made to each other during the 6.25 war. When the "entertainment soldiers" unit was disbanded in August 2013, Kim was reassigned to a frontline combat unit of the 12th Infantry Division headquartered in Inje County, Gangwon Province.