In the city of Orario, beneath an impossibly tall tower, lies the dungeon. Only adventurers who form partnerships with the gods themselves have any hope of defeating the monsters that lie within. But the dungeon is not the only place where monsters exist. Far from Orario, in the ruins of an ancient city, a new threat arises. To counter this threat, the goddess Artemis has come to Orario in search of a champion—but it’s not Ais Wallenstein (the legendary Sword Princess) nor Ottar (the strongest warrior to ever enter the dungeon) that she chooses. Rather it is Bell Cranel, a newbie adventurer partnered with a low-tier goddess.

Shirou Emiya finds himself an unwilling participant in a deadly competition where seven Mages summon heroic spirits as servants to duel each other to the death. They compete for the chance to make a wish from the Holy Grail, which has the power to grant any wish. Shirou is unskilled as a mage and knows nothing of the Holy Grail War, but he and his servant, Saber, enter into a temporary partnership with another Mage, Rin Tohsaka. However, problems arise between Shirou and Rin's servant, Archer, who seems to seriously despise him.