Taxi Driver (Season 1 & 2)

Kim Do-gi is an honest Special Forces officer whose life is shattered when a serial killer brutally murders his mother. Unable to find closure through the judicial system, he is recruited by Jang Sung-chul to work for Rainbow Taxi—a secret organization posing as a standard taxi service. Rather than just offering rides, the company operates a specialized "revenge-call" service, delivering vigilante justice on behalf of victims who have been failed by the law.