Set in the near future after the Japanese government has passed the Vengeance Act, a law which legalizes revenge killing, the series focuses on the members of the Special Execution Team of the Judicial Police Force, known as Sukedachi-nin (助太刀人, "Avengers"). These so-called Avengers are tasked with seeking vengeance on behalf of the bereaved by executing criminals using the same methods they themselves used on their victims.

The series consists of two parallel serializations, one in Shonen Gangan and one in Gangan Online. The Shonen Gangan series focuses on Avenger No. 9, Kōta Kiyodera, a kind, passionate man who strongly sympathizes with the victims for whom he seeks revenge. The Gangan Online series focuses on Avenger No. 8, Ryōko Koizumi, a young woman described as an angel who descends on the avenging fields to enforce the Vengeance Act. Other members of the team include Avenger No. 0, Captain Kamui Oda and Avenger No. 7, Yūji Yamagishi.