Demon King's Downfall

In the beginning, four beings ruled the world. They call themselves Entities. These creatures use their immense power to protect mortals from beasts and nature itself. And in return, the mortals built cities and shrines around them. For centuries, the world was at peace, until the fifth Entity was born. They called him the Demon King. It is said that his power was so dark and fearsome he could end the world. Terrified of the Demon's King strength, the four Entities combined their power and imprisoned him for all eternity. With the Demon King defeated, everyone lived happily ever after. At least that's how it was supposed to go....