The protagonist is a policewoman working in Shinjuku, a city that has become unsafe after a series of violent crimes known as the "X-Day Incidents". While responding to a call late one night, an unknown assailant attacked her, and when she regained consciousness she had a collar with a poison delivery mechanism, capable of being activated remotely, around her neck. Amidst the chaos and right before the protagonist’s eyes were men with suspicious backgrounds. They’re all part of an organisation composed of former police officers and have taken it upon themselves to investigate the brutal cases. Without knowing whether she should trust these men or not, she suddenly became the person who held the key to this massive case. In order to remove the collar that places her at the edge of death and to liberate Shinjuku from the malice that binds it, she cooperates; beginning to investigate the incidents with the men. Who holds her life in their hands? Will Shinjuku ever return to its former glory? [Translation of the official website's story summary.]