Date: 2451285 (October 12th, 2451 AD)
The future is not what we wanted it too be, sadly. March 3rd, 2077 was the end of civilization as we knew it in a war known as Ragnorak. The whole war was over in half-an-hour, but in that 30 minutes 2/3rd's of humanity was wiped out as the nations of the world unleashed their nuclear, biological, chemical, quantum, and memetic weaponry.
And what was left was hardly livable. The human race now lives in underground bunkers, only clinging on thanks to cloning and advanced biomedical research into arresting aging. The death rate has been slowed to a crawl, but the birth rate is non-existent. 90+% of the current survivors are now so sterile they don't even develop secondary sexual characteristics let alone a sex drive.
You however are different. You're one of the few people that is at least fertile enough to have a sex drive. Pregnancy would be unlikely, but enough of the hormones and enzymes work inside you that you grew into quite the beautiful woman- almost a throw back to a healthier time.
And the scientific minds between the bunkers think that may just save the human race yet. . .
[OOC: Alright, the story is that your character will be given the keys to a time machine in hopes of gathering fresh DNA in hopes of saving humanity. She won't be allowed to change history, that would cause too many paradoxes- but aside from missions given occasionally, she'll have a fair degree of freedom as long as she causes no paradoxes. At least, at first. . .