The Sunder-Sea was created when the star physically ripped the continent apart, drowning entire pre-war cities in an instant.
The Lore: Because the Sunder-Sea is plagued by wild-magic tempests, the barrier between the Material Plane and the Ethereal Plane is completely frayed across the water. Sailors report a phenomenon called "Ghost-Leaking." During heavy storms, phantom versions of pre-war towers, bridges, and markets will temporarily manifest out of the black water, solid enough to crash a ship into, before vanishing back into the mist hours later.
The Impact: This turns the sea into a shifting graveyard of ancient lore. Treasure hunters from Stormwatch Bay constantly monitor weather patterns, waiting for specific tempests to strike so they can sail out and scavenge historical vaults that only exist for a few hours at a time.