Die Bad

The first of the film's four parts is titled Rumble. The events start with two groups of rival teenagers hanging out in a bar, playing pool. They end up fighting and the main character Park Sung-bin accidentally kills another youth. He is thrown to prison for the next seven years.
The second part is titled Nightmare after the dreams Sung-bin still has about the man he killed. Sung-bin is trying to get back on track after being released from prison. He manages to get a job in a garage with the help of his brother, but his father still seems to loathe him for his past misdeeds. Eventually Sung-bin ends up saving a local crime boss, Kim Tae-hoon from a brutal beating and gets a job from him.
The next segment, Modern Man, intermixes fake documentary style interviews with a long fight between Kim Tae-hoon and Suk-hwan, an old friend of Sung-bin who was with him on the night that Sung-bin killed the man. Suk-hwan is now a police officer and his part of the interview tells about his job fighting crime while Kim Tae-hoon's interview segments show him speaking about his career in crime.
The last, longest segment is titled Die Bad. Sung-bin is taking control of his own group after Kim Tae-hoon is taken to prison. Sung-bin recruits a gang of youths, including Suk-hwan's brother, to serve as knife fodder in largely meaningless fights. In the end, Suk-hwan confronts and kills Sung-bin, but his brother is also killed.