In the near future of a fictionalized Japan under wartime, the ancient 'Act of Vengeance' is revived and professional executioners are permitted to kill criminals by the requests from their victims. People who are to be executed are notified of the execution time and date in advance and they are allowed to have their own guard.
Hiroshi, 29, is hired as an assassin at the 'Katsumi Vengeance Agency' for his precise shooting skill and his cold calm nature. Hiroshi meets his colleague Higuchi, 24, another agent who has put a hit on a young man named Toshio as Toshio's father has committed an atrocious war crime as a scientist and killed her parents. Hiroshi and Higuchi soon come to rediscover a traumatic incident that they share in their past.
15 years ago, Hiroshi, then a 14-year-old boy soldier, was under survival training in the woods. As he was lost and separated from the troop, he found a certain section of the forest being frozen unnaturally and his colleagues' bodies all piled up in a mountain. This atrocity was the result of an experimental bomb conducted by Toshio's father. Hiroshi also found a lone girl who has survived the bomb and she turned out to be nonetheless Higuchi. After that day, both Hiroshi and Higuchi have lost their ability to feel as a side effect from the bomb's radiation and thus made them perfect candidates for the 'Katsumi Vengeance Agency'.
Not long, a warrant is also issued for Higuchi herself. Will Higuchi execute Toshio? Will Hiroshi be able to save Higuchi from being executed? But the most important question perhaps is will Hiroshi and Higuchi ever be able to regain their humanity?