Hangyaku no Beretta ~Ingoku ni Ochiru Senshi~

Enter a future world ruled by the culmination of biotechnology, which has its roots in the second half of the 20th century.
Mankind aspired to become gods, and so they created the replicants, artificial copies of themselves, whom they put to manual labor, sent to war as expendable soldiers and used at obedient slaves.

Then, the appearance of a single man changes everything. That man is professor Albert, who instigates a rapid evolution amongst the replicants. The replicants revere him as a god and declare war on what they call the "worthless humans". A great war erupts in which the replicants attempt to erase the utopia the humans created for themselves.

Before long, the entire world lies at their feet. Then a savior appears who stands and fights for humankind. This savior is Beretta, the only replicant who was not driven mad by professor Albert. Her battle is about to begin!

[From DLsite English]