The Bully In-Charge

Briefly about The Bully In-Charge manga:

The protagonist, Kwon Dae-goon, works part-time at a convenience store while studying for a qualifying exam after dropping out of school. While moonlighting at the shop, he gets into a fight with bullies. Dae-Gon, who easily taught them a lesson, receives an offer from an educational foundation to take over the Iljin Management Project. After much deliberation, Dae-gon accepts the offer and joins the high school associated with the foundation. It is now up to him to defeat the school’s bullies one by one, at the behest of the education foundation.

The Bully In-Charge manga. 

After dropping out of school, Kwon Daegun is preparing for his qualification exam. While working a part-time job in a convenience store he got into a fight with some thugs. Daegun, who easily overpowered them, is offered a project called “Iljin in Charge/The Bully In Charge” by the Educational Foundation, which has been closely watching him for a long time. He, who accepted the offer after much consideration, enters a high school that belongs to the foundation and defeats the core bullies of this school one by one according to the order of the foundation.