Ten years ago, a mysterious spacial anomaly known as "Hell's Gate" appeared in Tokyo, altering the sky and wreaking havoc on the landscape. The real stars disappeared, replaced by false stars. During this time, people possessing various special abilities emerged, each capable of different supernatural feats - these are known as Contractors. Each Contractor has a corresponding fake star, which reacts to their activities. As such, Contractors are usually identified by their star's Messier catalogue number.
Following the disastrous Heaven's War, the United States lost its dominant position as a superpower to a mysterious organization named the Syndicate. The story revolves around a Chinese contractor codenamed "Hei" as he undertakes various espionage and assassination missions in Tokyo under the direction of the aforementioned Syndicate.