[It's okay- to her, this kind of thing is ancient history, she's not bothered by explaining it.]

Monsters have only very recently rejoined humans on the Surface, back home. Before that, we'd all been magically sealed underneath Mt. Ebott for... well, millennia at least.

There was a war, you see, in the far past between monsterkind and humanity. Monsters lost quite thoroughly. I'm afraid I don't know much about the details, that was all long before my time.