Sven Vollfied, a sweeper, is hired to investigate a matter concerning an election and is witness to an assassination by the Chronos corporation. The corporation sent their best man, codename "Black Cat", to do the job, and the assassin finishes the job with cold, calculated ease.

However, things are not all well, even in the large and powerful corporation known as Chronos. Black Cat himself eventually deserted the corporation and is joined by Sven in releasing the nano-bio weapon Eve from a black market dealer. With Rinslet completing the group, they travel around working as sweepers.

But there are darker shadows in the horizon, and our intrepid gang may find themselves fighting for their lives against supernatural forces who are most interested in Chronos, or, to be more specific, their top ranked assassin, Black Cat.

Chronos is eventually wiped out and years later Eve, Train and Sven find themselves needed in this gloomy city, all three of them drawn to it by the strong urge to clean the streets up and keep it that way. Meeting up they begin diligently working towards their goal of eliminating all crime in the Yuji territory.

They find that it is possible to do alone but would be much easier with help, train suggests that they invest in a building where they could prepare future bounty hunters with the special skills and knowledge they will need to aid in the war against crime. Thus forth the Chronos city academy was established.

To all of those passionate about justice we bid you step forth and join the academy, for those of you who manage to pass the training at the academy you will find yourselves with great knowledge and wonderful rewards.

A warning to the rebellious, you are very much welcomed in this city but realize that rule breaking will be dealt with very harshly.

Sincerely your erasers,
Eve, Train Heartnet, and Sven Vollfied