[It's a long story. But she has nothing better to do, surrounded by the ruins of a world that looked very much like her Earth. And he had put up with her attitude, had given her information about his world, which seemed dreamlike and intangible to A2 but surely must exist.

She focuses on the tedious repetition of picking up rubble, pushing it off to the side. Rinse and repeat.]

There was an alien invasion on Earth, a long time ago. [Long before YoRHa had ever existed.] They were responsible for creating machines, which overpowered humanity. After that, androids were made to stop the machines.

There's been fighting since then.