Rent The City of Violence (2006)

Detective Jeong returns from Seoul to attend the funeral of his long-time friend, a reformed small-time mobster, Wang-jae. Following a nostalgic reunion with his gang of former childhood buddies, he becomes obsessed with investigating the circumstances surrounding Wang-jae's death. What he uncovers sparks a chain of events that result in Jeong and his buddy Ryoo being forced to battle it out with teenage gangs, deadly assassins and a horde of murderous mobsters as they get closer to the truth.