[Well, she didn't flip about the flames, so her lack of reaction is... almost expected at that point.]

Earth. ... well, technically "Assiah". See... there's two sides to our world - Assiah and Gehenna. Assiah is the normal world, the one I was raised in, but Gehenna is the demon world.

It's kinda like two sides of a mirror, yehknow?

[It's a weird way to explain it, but that's how Shirou told it to him.]