After fighting with humans for over two hundred years, the Demon King became so feared that no one dared to challenge him anymore. He had strong knights and mages loyal to him and he owned a castle built just for him. However, he was not satisfied...he wanted to fight. When the Demon King realized that he doesn't have a long time left to live, he decided to raise a hero himself. "I will raise anyone who will enter the castle next to the strongest hero ever lived!" Then a young woman enters the castle--who is not even able to draw her sword. "She is the one!" The Demon King declares. So, the "Hero Raising Project" began. No one knew...that this girl, Erin, would be the one to reveal the Demon King's secret...