Illusia and his companions fight their way through the royal castle and are finally faced with the slime with the "Voice of God"—the Demon King. The slime pummels Illusia and his companions with powerful attacks he has stolen from others, but our heroes manage to defeat him. Or so they think. The slime that should be gasping for his last breath evolves into the legendary L-rank monstrosity, threatening to swallow everything with destruction magic. Illusia's companion has a plan, but will it be enough to save them?