Juvenile Offender 

Yun-Seong Lee is a victim of school bullying and decides to take revenge on school bullies by becoming a juvenile offender. After he enters a juvenile detention center, he meets a couple of guys who bullied him at school and executes his plan accordingly. However, there is one person who is yet to be avenged. Against these products of a failed judicial system, Yun-Seong's path of revenge begins. (Source: WEBTOON, edited)