Quote Originally Posted by ObsidianFire View Post
I'm just saying... when the only source of a phenomena is someone Flooding a Shard with Light or Dark... none of that is how a world "normally" works. And in-game citations for a lot of these sin eater claim would be appreciated.
The raid storyline makes it clear that if they stayed in the Empty for too long they would turn into Sin Eaters. The Empty was created by Eden passing through and passively performing its function of transitioning all aether in its vicinity to extreme astral polarity. Minfilia stopped the Flood by asserting control over it with the help of the First WoL souls and putting it to sleep.

Given that Ardbert says that their world had always been tipped toward light then it makes sense that it was so due to the presence of Eden. Though by the way things look is that while Eden is slumbering it takes a lot to get it to wake up and start performing its functions. Which means it could have been passively sleeping for a long time, ever since the Sundering, but even while it is sleeping it is still performing its passive functions. Which means that any entity that wandered near it would see itself become a sin eater as its elemental balance gets disrupted and goes all towards astral. Which is how people get converted into Sin Eaters, by all of the elements that make up their body going astral. This is why victims hit with "light seeds" turn into Sin Eaters, because thanks to a cluster of light sending their entire elemental balance towards astral their body struggles to stabilize its elemental balance, so long as they kept receiving light aether the body would eventually be overwhelmed.