In a guys-only world

Core backstory:

About three generations ago, there were men, women, and “mixed-ups”, when people were not so obsessive about having sex.

Everything changed however, when an unknown plague spread among the human race. Due to its symptoms, males were naturally immune to the plague, whilst the other genders would gradually become males. It was not brutal but fatal to the human race, if the situation become out of control.

There was none but one antibody discovered, which was the human's semen, and one dose would take effect of about one week. Due to this fact, though the plague never had an official name, the general public often called it the man plague. Everything seemed under control at first, but soon the plague showed resistance to the antibody and the effect of the semen became weaker.

The last known human vagina disappeared three years after the discovery of the man plague, which belonged to a woman called Cassy Jones, later known as Kevin Jones, who recorded her last days in the self bibliography, which vividly described her ever lasting orgies, yet still couldn’t retain her female traits. Cassy was not a minor case, and during the three years, whilst sex became a common social activity, normal production lines generally stopped. More over, monogamy became less accepted and group sex happened more often. There was a time when birth rate increased dramatically, while only a few weeks later, the rate of young people also reached its peak, due to the lack of food. Another side effect was that gay sex become more accepted — what else would you expect when tens of men vs. one woman.

Lucky for men, the procreation finally recovered after a ten-year gap, when a faction called the PART a.k.a. Post Apocalypse Re-procreation Technologies was found by the Union Government of Post Apocalypse. However, the details are kept secret. The only fact exposed to the civilian is that every man have the duty to donate his semen to the PART once a year after 21. The first generation once suspected that the “procedure” might violate the pre-apocalypse ethics, but such voice vanished among the later generations, since they themselves are raised by the PART. Young men are raise in numerous reservations in order to be kept from the now society filled with sexual activities. They are taught about sufficient knowledge of sex of course, but only in educational term. But when grown up, they are to leave the paradise, and all their later lives are depending on themselves.