A hero journeys to the Demon Realm, seeking the legendary "Demon King’s Sword", to save the Kingdom's princess from forced marriage. But the Demon King, intrigued by the hero, desires her for himself, but she remains loyal to the royal family. In a cruel twist, the Demon King assumes the form of the princess, breaking the hero. Captured and imprisoned, the hero lives out her days in the Demon King's castle, trapped in the delusion that he is her beloved princess.