Dokgo Rewind (2018)

Kang-Hyuk (Sehun) is good at fighting. He has dropped out of school and hangs out with his two friends who are also dropouts. One day, Kang-Hyuk saves Kyu-Soon (Yoo In-Hwan) from some disorderly students. Kyu-Soon ask Kang-Hyuk to teach him how to fight. Kyu-Soon explains that he wants to protect his younger sister Hyun-Sun (Kang Mi-Na). Kang-Hyuk accepts the offer for help and they become friends. Later, Kyu-Soon is beaten to death. Kang-Hyuk decides to take revenge on the students responsible for Kyu-Soon's death. Jong-Il (Joe Byeong-Gyu) and Tae-Jin (Ahn Bo-Hyun) are also sick of the violence caused by the disorderly high school students and join Kang-Hyuk.