#i also havent played the scarvi dlcs so if this has already been contardicted in there uhhhh. nuh uh

[nemesis-is-my-middle-name]

before legends ZA comes out and totally destroys my going hcs i guess i should say my piece, anyway i think X is the "canonical" game bc fairies, BUT, i also think that, while xerneas has historically been kalos' patron deity, yveltal was actually galar's. and much like how deities irl can get telephoned around over time, while yveltal's power over death was always... present, to galar, it wasn't the ruler of death. it represented conquest and victory, to them. it was only after yveltal fell into its cocoon and was slowly forgotten that the kalosian interpretation of it as death became commonplace.

relatedly, the kalos war that happened 3000ya was a war between it and galar, which ultimately culminated in the firing of the ultimate weapon and the darkest day, which were actually a singular event. and the war was centered on the great crater, and the region around it, which wouldn't become paldea for another thousand years. they were both interested in it bc yveltal and xerneas are both believed to have originated from the crater (see: xerneas' crystal horns) & therefore it's both religiously significant and a source of great physical power—the ultimate weapon was actually built using a scant few fragments of crystal recovered from the crater directly. (though the great crater has always been super impenetrable so they were gathered at great cost from the very upper regions & this is not a feat kalos could probably repeat)

also, it was only after the war ended that zygarde appeared. zygarde's always an enigmatic figure, but in essence it's the crater's cleanup crew. it scavenges divine energy to bring back. this is also why it shows up in alola.