Farland Story Denki: Arc Ou no Ensei

After Arc and his friends have defeated the evil Demon King, the brave knight was chosen to be the next king, and the lovely priestess Ferio agreed to be his wife. On the day of coronation, Arc and his little sister recall the events of the grand battle, when suddenly they hear a noise from the shrine with the Hole Sword. When they rush there, they find out the sword was taken away by demons. So, was the Demon King not defeated by Arc after all?