War. War never changes.
The 21st Century was a time of great change in the history of man. Empires which had stood for a thousand years gave up their last breaths and died quiet deaths while new ones rose to take their place, and great men and women of legendary will and charisma shaped the future of the human species. But it was the absence of nine young women and one young man which made the most difference of all. The legendary Sailor Senshi and the lost Atlantean prince Endymion failed to reincarnate as had been foretold, but their eternal enemies, the Dark Kingdom, did not. The foul armies of Queen Beryl and Metallia swept over the Earth in the absence of early opposition and established a solid foothold on nearly every continent before the armies of man were able to rally enough to halt their advance. When it became clear that Beryl's forces were winning and all other options had been exhausted, man turned to their greatest and most terrible weapons, and purged the Earth of Metallia's taint with nuclear fire.
That was 200 years ago. Beryl's armies are scattered and broken, her generals dead and Metallia itself returned to slumber. But the human race is no better off; her great cities are broken, nations are a thing of the past, and the planet itself is shattered and torched beyond all hope of repair. Hope itself is a commodity few can afford.
Mizuno Ami knows nothing of Beryl or Metallia beyond what she's read in what few history books Vault 101 has available. What she does know is that her father has left the secure underground Vault which has housed them all her life for some purpose out in the barren wastes of the Capital Wasteland. What that purpose is, Ami doesn't know. But Ami has always been an inquisitive girl, never able to leave a question unanswered, and so she strikes out into the wastes to find him and demand an explanation.
Ami's quest nearly ends before it can begin when she encounters a band of raiders outside the city of Megaton, her story very nearly ending in death or enslavement but for the intervention of fate and a small black cat. Her fortunes are reversed in an instant when Ami is blessed with the power of the planet Mercury, a sacred power unlike any which has ever been seen in the Capital Wasteland. In exchange for this power and for saving her life, her savior asks a favor: find Princess Serenity, she who possesses the Silver Crystal, and who holds the power to lift the remnants of man out of the wasteland and into a crystalline paradise. Assuming the wasteland hasn't already eaten her alive.