Inside the silent, ruined castle. Standing lonely in a desolate land far from the city, this decaying place looks like no one could possibly live there when viewed from the outside.

However, someone is imprisoned here. The King of Demons, who once plunged this world into the depths of terror. Most of the common folk believe the Demon Lord died that day, defeated by the Hero. But though their power was lost, the Demon Lord was still kept alive.

...More accurately, they simply wouldn't die. The King, unsure of how to handle the situation, had the Demon Lord sealed in this ruined castle and ordered the Hero's party to continue monitoring them. Normally, a Hero who had already completed their quest might not have been obligated to take on such a task. However, the Hero accepted. The King was pleased, seeing it as a sign of the Hero's sincerity and loyalty, further elevating the Hero's reputation. But the reality of the situation was—