The United States has seen an increase in mafia-related activities, including assassinations that take place regularly on its streets. A mysterious company called Inferno is believed to be responsible for these criminal acts through their use of a highly advanced weapon known as "Phantom." During one such murder, a Japanese tourist unintentionally witnesses Phantom's latest killing spree. Fearing for his life, the tourist takes refuge in a secluded building. However, it is revealed that Phantom is actually a young woman named Ein and the leader of Inferno, who goes by the name "Scythe Master." The tourist is captured and brainwashed, given the name "Zwei," and becomes a puppet controlled by Inferno with no recollection of his past. As Zwei, he finds himself in a world filled with lies, deceit, and violence, fighting to stay alive while hoping one day to regain his memories and break free from this deadly cycle.