The Flood of Light destroying Nabaath Areng in Amh Araeng.
The Flood (氾濫, Hanran?) is a term from Final Fantasy XIV relating to an imbalance between elements that causes one to expand and consume a world. A similar concept exists in Final Fantasy III.
The purpose of the Floods, as orchestrated by the Ascians, is to rejoin the different reflection worlds of Etheirys to the Source, bringing back their society and reviving their god, Zodiark. To do so they cause one of the elements in a world to go out of balance, and at the same time cause a Calamity of the same element on the Source. This breaks down the barriers between worlds and causes the reflection world's aether to be absorbed back into the Source. However, if the world is completely flooded without a corresponding Umbral Calamity in the Source, as happened in the Thirteenth and nearly did in the First, that reflection becomes unable to rejoin and therefore useless to the Ascians' plans.
History[]
In the past, the Ascians attempted to conduct a rejoining between the Source and the Thirteenth by increasing that world's darkness. The resulting Flood of Darkness ruined the Thirteenth and turned it into the World of Darkness with its residents reduced to voidsent, causing the Ascians to rethink their method.
When the Ascians targeted the First, they exploited Ardbert and his comrades into increasing the amount of light in their world for it to be consumed in primordial light. Though Minfilia Warde stalled the Flood of Light from consuming Norvrandt, it had already claimed most of the First while turning those caught in it into sin eaters. Beyond Norvrandt, the rest of the First became known collectively as the Empty, due to it being scoured by the Flood of Light.
The Ninth reflection, the unlost world, was slowly consumed by lightning aether over centuries, beginning one thousand years ago, which caused endless thunderstorms across more and more of the planet. The original cause was unknown, though it was likely another attempt by the Ascians to begin a rejoining. 400 years ago, a superweapon created by Lindblum triggered the Storm Surge, a Flood of Lightning that overtook the entire planet. The only known survivor was Alexandria, which took in what refugees it could from its neighbors and was able to keep its capital safe inside a dome. When the Warrior of Light learned about this world's history, they compared it to the First and Thirteenth. By the time they visited, the Storm Surge had ended.