5012 A.D. The year mankind's glorious history came to a sudden and abrupt end... when the world was invaded by aliens from beyond the stars. The aliens unleashed a new breed of weapon—machine lifeforms—that all but annihilated human civilization. The handful of survivors that remained fled from Earth, seeking refuge on the moon.

5204 A.D. Humanity launched its counterattack, deploying an army of androids from a network of orbiting bases. But after more than a dozen large-scale descents upon the enemy, we still haven't managed to repel the invaders.

That is why you, the YoRHa forces, exist: To break this stalemate once and for all. You are our ultimate weapon...and you must put an end to this war.