The Divine War
And so Asavla became the battleground of the gods
The Divine War is the common name for a particularly prevalent myth, detailing a centuries long battle between Kysro, Goddess of Darkness, and Ylais, Goddess of Light. While the middle of the story remains very similar from telling to telling, the cause of the conflict and the final outcome vary somewhat between religions and culture. Some say Kysro was the winner, others claim it was Ylais, and others claim the war drew to a bitter stalemate that continues to this day.
In the simplest re-tellings, Kysro and Ylais find themselves on opposing sides of a vast, century spanning conflict. The world of Asavla became their battleground after the two collide with it, killing all life on the planet and leaving it barren. Eventually, the two cease to fight, though whether it is due to victory or truce varies.
The sudden death of all life on Asavla far back in the planet's history appears to have strong evidence to support it, such as a dearth of fossils dated past some years, and the sheer number of similarly aged corpses in disparate locations.
The site where Kysro and Ylais collided with the planet is suspected to be the Crater Sea, one of the deepest parts of the ocean and possessing many of the characteristics of a meteor crater.
Additionally, the gods are considered a known quantity - they have appeared through oracles throughout the years, and their magic is present through the demigods.
The Divine War is a myth known throughout the world, as it travelled through the gods themselves rather than the spread of people.
Variations & Mutation
One place for variants is the motives of the gods - did they fight for greed, revenge, honour? The gods themselves appear unclear and conflicted, and evidence suggests they may have changed their answers over time. A common Kysroan variant is that Ylais had stolen something precious, such as a prized divine artifact, and the war revolved around her trying to get it back. Conversely, Ylaisan variants claim that Kysro tricked Ylais into giving her power, and that Ylais fought to have it returned.
The ending also varies wildly. Kysroan variants claim that Kysro won narrowly, ushering in a perfect age of darkness for thousands of years from which humanity arose. Ylaisan variants say the opposite, and that a thousand years of light reigned and heralded the birth of humanity. Some later variants from both religions have added the idea that the gods remain trapped on Asavla, either due to exhausting their power or as punishment from a broader pantheon of gods unknown to humanity.
In modern times, efforts to reconcile the conflicting myths have led to a 'draw' narrative, wherein the gods equally wrongs each other and fought to a bitter draw, never conceding defeat. And that, by fighting till the tired end, have trapped themselves on Asavla for the foreseeable millennia.
In the absence of a widespread creation myth, the constancy of the Divine War is very important to many people. It serves as the start point of the world they know, under the watchful eyes of Ylais and Kysro, and it's one of the things that can be shared cross-culturally and cross-religiously, if you tread carefully enough.