It's a long story. [Rita scratches her chin, trying to think of how to condense it for someone who knows nothing of her world.]

Basically... a certain technology we've been using, which runs on aer, turned out to be upsetting the balance of aer throughout the world. This caused tons of problems, including the slow destruction of ecosystems, plants growing out of control, and monsters growing more aggressive than ever.

The worst of it, though, was that it led to the appearance of the Adephagos... magical beasts that mindlessly consume life. The first time they appeared, the ancients managed to drive them away and put up a barrier around the whole planet to keep them from coming back, but some idiot broke the barrier, and now a whole swarm of them is headed our way.