The C-line was a line of genetic slaves bred by Manpower Incorporated of Mesa. C-line sex slaves, both women (A-variants) and men (B-variants), were among the company’s most popular breeds, always in demand on the market. Their genotype had been selected and shaped for physical attractiveness and for as much in the way of libidinal energy and submissiveness as the Mesan gengineers could pinpoint in the genetic code. Developing C-lines were subjected to rigorous training, including forced sex training starting at the age of nine, which was called the "Phenotype developmental process".