Maintaining a delicate balance of power, the kingdoms of Amoria, Ishilfen, and Vanrodis rule over the continent of Kuna'anh. Even the slightest hint of trouble in one country could spark a continent-wide war. However, their one common fear is the evil dragon Daganzord, whose only meaning of existence is to devour and destroy all life. Ten years ago, a group of mages worked together in an effort to seal away the malevolent beast. But the ritual—later known as the Balbagoa Tragedy—was a failure, and many lost their lives. Though his parents died in this tragedy, Hiiro was saved by the swordsman Giruu. Under the latter's tutelage, Hiiro learned swordsmanship with the sole purpose of seeking revenge. Now a budding master himself, he sets out in search of Daganzord in order to realize his long-awaited vengeance, or to be consumed by the dragon and meet the same fate as his parents.

Six months have passed since the victorious Battle of Britannia and the reclamation of Gallia from Neuroi invaders. Yoshika Miyafuji, member of the famed 501st Joint Fighter Wing, has come back home to Fuso and graduated from middle school. However, her fight is far from over. She receives a letter supposedly sent by her long-deceased father, containing blueprints of a state-of-the-art Striker Unit he had been working on before his death. The Unit, designed specifically for Yoshika, might be capable of harnessing her extraordinary magical powers. Meanwhile, a new threat in Europe is rising. A Neuroi nest of an unprecedented size and might has appeared over Venezia, wiping out local Witch forces and instantly swallowing the northern part of the country. To make matters worse, a newly spotted humanoid type of Neuroi is attempting to come into contact with humans. Yoshika, incapable of abandoning her friends on the front lines, must once again venture to the war-torn continent.

In the American city of Snowfield, a new Holy Grail War is about to erupt. Such ruthless confrontations pit against each other magic experts known as magi, who ascend to the status of Master by summoning Servants—heroic spirits of the past. The winner is thought to have any one of their wishes granted. However, it appears that the organization behind the present situation has merely managed to create an imperfect copy of the Third Holy Grail War. As the unusual ritual catches the attention of the Mage's Association in London, Flatt Escardos, the young apprentice of Lord El-Melloi II—a former participant of the Fourth Holy Grail War—travels to Snowfield and, to the great dismay of his teacher, joins the ranks of the Masters. In this fake conflict where the line between Masters and Servants is blurred, the different factions will have a hard time preventing the city of Snowfield from plunging into total chaos.

While saving a child from harm, otaku Asahi Ikusaba is transported to another world and believes he has reincarnated with cheat skills similar to those of the characters from his favorite games and novels. Unfortunately, reality strikes when an encounter with a powerful monster shows that he is still nothing more than an average person. In this moment of extreme danger, Asahi instinctively calls out to his overly doting sister, Maya, who appears out of nowhere, possessing the overpowered abilities he thought he had. Maya is ecstatic to see her brother again and resolves to use her newfound powers to protect Asahi no matter what. Together, the close-knit siblings attempt to find a way back home while enjoying their new lives. However, it soon becomes clear that their arrival in this world may have had a purpose. With the Demon King's overwhelmingly powerful army approaching, no one but Maya seems to be able to stand in its way.