Chapter 0: Prologue.

In the future, humanity has invented interplanetary spaceflight and begun to explore the galaxy. In doing so they encounter an alien race, commonly referred to in later history books as the "Engineers".

Engineers have caught the signal human sent to outer space and discovered there was another intelligent race in the vast universe. As for humans, they remained to be cautious and just sent a small team to contact.

However, the discovery of an Engineer base in the asteroid Eros led to a war between the two species. From the human messenger, not only they found that humans and Engineers were compatible enough to breed with each other, but the result descendants were much better than normal Engineers. Humans saw the recorded video and decided this was a declaration of war.

Engineers were good at multiple aspects of science, but their specialty was biology. They didn't use mass-destruction weapons, but biological weapons instead. A virus, which was called FEMVID (feminization virus disease), was released into the atmosphere. It caused gender-changing in human males, transforming them into females with hyper fertility as well as extra libido. Moreover, once the patient was impregnated, they could never turn back.

Because of the advantage of number, humans narrowly won, resulting in the discovery of advanced alien technology, including virtual reality, gene manipulation, and so on. But the leaders knew that sooner or later Engineers would return with a much larger force. Ostensibly in preparation for another invasion, an International Fleet (I.F.) was established on Earth, which created a Battle School in Earth's orbit to develop gifted children into commanders capable of defeating the Engineers in the next war.

The war also caused some changes in social standards. From the data in that base, scientists have successfully created a vaccine for FEMVID. But due to the lack of resources, just a limited amount was produced. Therefore, only men who displayed sufficient levels of fecundity, stamina, and intelligence were allowed to breed. To keep the world from over-populated, each family could only have two children at most. The punishment for having a third was severe.