Centuries ago, the Surface Wars devastated the planet. Nuclear and geothermal experiments ruptured the crust, releasing superheated gases that melted polar caps and flooded continents. Humanity's remnants sought refuge beneath the ocean, where scientists constructed Aqua Arks—massive domes and caverns designed to sustain life. Over time, the domes fractured or merged with natural underwater cave systems, leading to scattered civilizations called Subrealms.
Now, generations later, the ocean floor is a labyrinth of bioluminescent cities, monster-ridden trenches, and portals—called "Rift Caverns"—that connect distant zones. Relics of the "Old World" drift among coral forests and ship graveyards, waiting to be rediscovered.