One hundred years ago, a war occurred between the Demon King and the Goddess that could have destroyed the world.
In the end, the Goddess was defeated, the heroes were sealed and the war came to an end.
No one knows what happened to the Goddess.
The Demon King also lost a great deal of magical power in this war, and was targeted at his weakest moment, and the Demon King was betrayed.
The traitors shared some of the Demon King's power with the lords of the Demon World, who sealed the four heroes, and reigned as the new Demon King, with himself as the pinnacle of the Demon World.
The remnants of the Demon King's lost power and body flew away to some ruins in the outside world, waiting for the day of revenge to come.​