34th Amendment
Stories in this universe are set in a misogynistic version of the U.S. where the 34th Amendment to the Constitution legalized non-hereditary slavery. People, mostly beautiful young women, are traded at auction houses like livestock and treated even worse, "voluntarily" indentured to pay off a defaulted debt or to evade jail - and in some cases just because of stupidity and misplaced trust. Getting officially "graded" at such an auction house for sexual attractiveness and "slave heat" after suffering rigorous training and abuse has become a rite of passage for young women, but one that all too often ends in enslavement for the naive girls. But in a world filled with cruel punishments and intense sex, their acceptance of their new role is usually only a matter of time.