The world is at peace, the demon king was killed by the hero, the monsters are slowly disappearing. Two hundred years after the hero was summoned and killed the demon king, the evil power that created the monsters vanished. But one day, on a deep cavern, in a pool of black water, the grudges and hatred of numerous lost souls created something.

Then, in that day, a new creature that would change the world was born, the black slime.