In the vast oceans between worlds, where the water had infinite depth, shapes turned beneath the waves and worked to force their way to the surface, with malicious intent. A mariner from an ancient world saw the darkness moving beneath his ship, and ran to grab his radio. The movement shifted the water and created a massive wave that smashed his ship to plywood.
The wreckage washed ashore some years later, on a desert world that never saw sunlight. A tribesman with a painted face and spear came across the wreckage and discovered that the sailor had recorded a message. The tribesman brought this message back to his friends, and they spoke it to one another, and word spread. And as the tribes formed cities, and the cities formed nations, the words of the broken ship grew in significance.
When philosophers rose, they debated the meaning of the words, of a language they did not understand.
When philosophers were replaced by religion, the religions all claimed that it was a prophecy, if only anyone could understand it.
When religion was replaced by science, they studied its linguistics, and ventured to the wrecked ship, discovering a miniature library. And they studied this archive, and slowly began to understand the warning. It was a warning! The religions claimed that it was the prophecy! They said that prayer must begin.
The governments of the nations decided that the threat was imaginary, but also decided to prepare. They outlawed travel on the high seas and began to construct massive weapons. They mined their islands and lands as long as they could, and constructed a fleet of cruisers and battleships. Wars were forgotten as they prepared for this massive apocalypse.
Many snuck out into the high waves, and began to worship. They were greeted by emissaries of these great beings. The great beings demanded sacrifice, and these worshippers returned to their world to collect. The governments split in two, those who believed in the sacrifice, and those who did not. A great war raged, in which even greater weapons were created to battle one another. By the end of the war, their resources were consumed, and so they decided to brave the waters to find this other world where this cryptic message had come from.
This desert world came across a forested world, and they quickly made war with those there. The forest-people were ill equipped, still just barely constructing firearms, and the forest-world lost its resources. And so the desert people continued from world to world, until they were sated. They decided to retrace their steps back to their original world, where they resettled their cities, content with their supplies.
A scout reports having seen great movements beneath the waves, and the desert world rallies its navy. It is time, they decide, to find this great apocalypse. Every man, woman, and child is found and gathered for this task. Each is taught how to operate some piece of their great machinery. Some of their ships require a thousand workers to keep working. Their weapons can smite worlds from existence at the touch of a finger.
This fleet glides into the open sea, where the movement had been seen. But the fleet comes to a halt, seeing nothing there. As the scout is being chided, sonar detects a massive object pushing through the ocean towards them. They had time enough to warm their weapons before it wiped them out.
The monster saw the smashed navy on the edge of its finger and shook it off into the waves.
