Mission doesn’t offer a battle you could point to and say this is the war, and this is what it’s about. It offers fog, and movement inside the fog, and the accumulated ghosts of wars that already happened layering in with whatever’s currently happening, until the distinction between a long-dead conflict and a live one stops being something anyone there bothers to track.
That’s the real content of the Land: not a fight with a shape, but endurance without a finish line. Shapes shift in the mist — you don’t always know if what’s moving toward you is a current combatant or a memory of one, and after enough time on Mission, you stop being sure the distinction matters to your survival either way. Old wars don’t end here so much as they keep contributing extras to the current one.
The preposition earns its keep in exactly this Land. You don’t live in Mission — that would imply walls, a container, something solid enough to trust between you and the fighting. You live on Mission, the way you’d say on a front, on a watch: exposed ground, currently held, with no promise attached to tomorrow. Everyone there has stopped bracing for the war to end and started, instead, just enduring the fog it left behind.