South Korea is the south side of Korea, opposite of North Korea, a democratic-based country.
It appeared in the Hawaii Five-0 Pilot (episode) where in the Pohang district of the country, future Hawaii Five-0 leader and Navy SEAL, Lieutenant Commander Steve McGarret was seen escorting Anton Hesse, an arms dealer to prison but unfortunately, the unit came under attack from a group who sought to spring Anton from custody.
Things took a turn when Anton escaped and prepared to draw a weapon, forcing Steve to kill Anton by shooting him dead while back in Hawaii, Victor Hesse, Anton's brother later killed Steve's father, John McGarrett much to Steve's horror.
In Kil'ilua (episode), the Hawaii Five-0 team of Detective Danny Williams, Lieutenant Chin Ho Kelly, Officer Kono Kalakaua, Agent Lori Weston along with Steve's mentor, Joe White and a lone Navy SEAL team entered North Korea via South Korea after learning that Steve had been kidnapped.