A long time ago, demons and humans got along. The prince of the demon kingdom and the prince of the human kingdom were best friends and hung out all the time. One day, the kings of both kingdoms had a fight and they became enemies and the princes were separated. Years later, Rui was the king of the Demon kingdom after killing his dad. He hates humans and wanted to take over their kingdom. One day, Rui got a notice from a servent that the humans were sending their head knight to duel Rui.