The World of Dusk is a representation of the world that existed before the crystal at the Crystal Temple was shattered, sundering it and the world into two halves: The World of Light, and the World of Darkness. Before the division occurred, each of the land's civilizations lived in general peace with each other. However, the growing might of the military-focused Avalonian Empire, led by the Emperor, began to cause difficulties for neighboring towns and settlements.
After a decades-long truce that had been brokered between Avalon and the Kingdom of Lux, the Emperor decided to renege on their treaty and sent four youths to steal the crystal from the nearby Crystal Temple, which was under jurisdiction of the King of Lux. The group sent to capture the crystal was later destroyed by the Watchbeast, the guardian of the shrine, who lost its senses and attacked it. This caused the planet to be split into the worlds of Light and Darkness.
Later, after the twelve crystals had been gathered, the two halves combined together once more to create the World of Dusk, a place reminiscent of the world that existed before the divide that is cast in the perpetual glow of twilight. However, the world was not as it was before, and many of the land's occupants and cities have simply vanished from the face of existence. Sophia, the elder of Mysidia, noticed the dearth of human life, and sent her disciples, Alba and Dusk, along with the remaining warriors of light and darkness, to explore the barren land and discover what had happened to its population.
The eight manage to locate eight pieces of Dark Matter, which they use to access Castle Avalon and open up a path to the void through its throne room. It is here that they discover the missing towns and its people, cast into the void as a side-effect of the Dimensional Shift. After confronting and defeating the Emperor in the deepest depths of the World of Nil, the World of Dusk is transformed once again, this time into the landscape that existed at the story's beginning.