The Errant war was started by the EnsigerumThe story told by Sarine is that one of the triggers to the war was a powerful half-elf mage who started babbling about invisible assassins and then destroyed a city. Everybody naturally assumes that he's just a crazy errant and that there weren't actually any invisible assassins. But what if he WASN'T actually crazy? Could the Ensigerum have been responsible for triggering the war in order to set the elves against the half-elves?
Humans were created by ExitialisFirst the Paedagogusi don't seem to have any idea what humans are or where they came from, and when in Senilis' resting place their dialogue implies that humans didn't show up until after Senilis and Anilis went to 'sleep'. Second future Meji outright says Exitialis did not end up like the other two, and that he's still around. As for WHY he'd make them, probably it's to do what Senilis and Anilis failed to do with their creations, and in fact it seems probable that the way half-elves seem to be able to suck up Senilis and Anilis is intentional on his part.
Humans ARE ExitialisExitialis isn't a "God of Death", it's a dead god... or, more accurately, a dissipating gestalt of one third of an alien race's collective individuals. When Exitialis "dies", the alien race that made him up reconstituted itself as individuals: the human race. Unfortunately all that knowledge that humanity held as a godlike gestalt intelligence didn't trickle down, leaving newly corporeal humanity as a savage child-race.
Errant Story is the ancient prehistory of the modern Poe-verseDoes Not Play Well With Others and Exploitation Now happen in the same universe, and elves appear in Does Not Play Well With Others. Also, the fairies appear in both in Errant Story and Exploitation Now, but they live forever and are immune to damage, so it's not surprising they're still around.