Jukji Aneuryeomyeon

A high school student, Im Da-Joon is used to being bullied at school. Right before he was about to end his own life, he saw the interview of a friend killer on TV by chance. He got impressed by the interview and decided to seek revenge. His revenge was successful, but his life went in the wrong direction… Im Da-Joon quit school and joined the group of teenagers who ran away from their homes. Da-Joon is now free from school bullies, but now he has to survive against the street gangs who are much tougher than school bullies.

(Source: YLAB)

Note: Belongs to Blue String universe.