For the first half of my gestalt build, I have a fighter 20 (Eldritch Guardian archetype) that specializes in weapons from the Natural Weapons group.

The second half is a wizard 15 (Spellbinder archetype), and Archwizard 5 (Prestige Class).

Do you each want to throw out a short (Fate-style) aspect for me to work into the starting world?

About a few hundred years ago, the mages of Talsant had come to a worrisome conclusion.  This particular conclusion had required about a century of being shouted down by "wiser minds," until, at last, a panel of young upstarts had prevailed at the 202nd International Parliament of Mages.

Their conclusion was that the world was ending.

Outside the conference, however, most folks shrugged.  It was not unusual for mages to talk about worlds ending, after all.  And it was apparently two hundred years away.

The world decided that at some point, they'd get around to it.

Later, the autocrats of feudal kingdoms realized that the end of the world would eventually create panic and, possibly worse, resistance to spending one's life shackled to systems of huge wealth inequality.

The autocrats pointed out that the mages had got it wrong. Or that they had overblown the problem. That the use of umbral energy was not, in fact, eating away at the barriers between worlds like some kind of corrosive acid. It was just eating away at it a little.  Planes didn't just crash into each other.  Use of some positive energy would fix it all. Songs were paid for, and bards popularized how silly the very notion was.

So at the 400th conference of mages, the world had managed to just about ignore the problem.