You are the Demon King. For three years you have reigned terror on this world to cleanse it. You've managed to do this as the Heroine, the one who was meant to form a party to kill you, decided to come singlehandedly without any teammates. Her powers make her unkillable however they cause her to almost entirely focus on killing the Demon King. As you sit on your throne, the portcullis that guards your room is slowly hacked down. The Heroine steps through it. It's over, Demon King.