The ruthless King Grey holds the title for the most powerful king ever, having eliminated anyone in his way with his incomparable strength and large army. One day, however, he is inexplicably reincarnated in another world—as an infant! Now renamed as Arthur Leywin, he also discovers that this new world is capable of magic.

As years pass by, Arthur gains invaluable knowledge of the new world and continues to hone his magic. Despite his young age, Arthur displays incredible magical talent to his parents, who decide to further cultivate his skills by taking him to a city. After being separated from his friends and family by an ambush, Arthur is saved by a strange life form named Sylvia, who offers to assist him with his magic training.

With Sylvia's help, Arthur is determined to find a way back to his family. Arthur's arsenal of magic and his new-found companions will allow him to defeat any danger that lies ahead.