Designated Bully is a Manga in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.designatedbullymanga.com fastest updating comic site. The Summary is

After dropping out of high school, Daegun Kwon is working part-time at a convenience store while preparing to get his GED. After being harassed by a group of punks during work and teaching them a lesson, Daegun is approached by a woman from the Education Foundation about a project called “Designated Bully.” After being offered another chance at a normal life, Daegun accepts the offer and attends school to perform his one duty as the designated bully: To take down the other bullies, and restore order to the school.