Asta and Yuno are orphans raised in Hage. When they reach 15 years of age, both of them received their respective grimoire and enter the Magic Knights squads. Asta goes to the Black Bull squad while Yuno chooses the Golden Dawn squad.
Asta, Luck Voltia and Noelle Silva of the Black Bull squad are assigned to explore and conquer a dungeon along with Yuno, Klaus Lunette and Mimosa Vermilion of the Golden Dawn squad. A conflict arises when they encounter the mages from the Diamond Kingdom.
Asta and Noelle Silva are invited to an awarding ceremony by Julius Nova Chrono along with Klaus Lunette, Yuno and Mimosa Vermilion after completing the dungeon exploring mission. During the banquet, the Royal Capital is being invaded by an army of the undead.
The Black Bulls get assigned a special mission from the emperor which to find a magic stone that the Eyes want. they discover that, that stone is in the Underwater Temple and immediately rush there but they will have a challenge to complete to obtain that stone which was given by the priest of the Underwater Temple. But in the middle of this challenge there is an interruption.....