Driven out from his orphanage, Nakajima Atsushi wanders the streets of Yokohama on the bring of starvation. Determined to live, a chance encounter with a drowning stranger changes his fate...

Despite joining the Armed Detective Agency, Nakajima lacks conviction that he'd be of any use. Just as he's about to bid the agency farewell, a bomber takes over the agency with one of the agency employees as his hostage...!

The Agency investigates a series of disappearances in Yokohama. Kunikida enlists the help of a hacker named Taguchi Rokuzou, but all they find are photos of the victims and mention of a mysterious figure called the Azure Messenger. They follow the trail of clues to an abandoned hospital...