Struggling to make sense of his broken memory, high schooler Hakuno Kishinami arrives at school with a piercing headache. Staring out of a window in his classroom, he notices two girls in the courtyard begin to fight. The force of their encounter shatters the windows, but to his surprise, the students are unfazed. An armor-clad man enters, slaughtering the students with his lance and sending Hakuno bolting for safety.

After escaping the frenzied knight, Hakuno realizes that he has become fully amnesiac, remembering only the words "Holy Grail War." Wandering the emptied school, he stumbles through the building until he is assaulted by two strangers. Bleeding out and surrounded by corpses, he clings for life with no sense of self.

As the pair of men move to finish off the dying Hakuno, a voice beckons to him. Snapping him back into reality, a woman in a vibrant red dress tells him that his end has yet to come. Identifying him as her Master, she draws her blade against the assailants, affirming a contract between the two that will carry Hakuno through the coming trials and tribulations.