In a world where an all-powerful Holy Grail fulfills desires, the Fourth Holy Grail War emerges, promising a different outcome with the Einzbern family's possession of a Grail vessel. The infamous 'Magus Killer' Kiritsugu Emiya is hired by the Einzberns and bound by marriage to their daughter Irisviel to compete in this deadly contest against six other participants. With ancient familiars and conflicting ideals at play, Kiritsugu, aided by his familiar Saber, faces his toughest rival in the form of the conflicted priest Kirei Kotomine. Fate/Zero delves into this ruthless battle for supremacy, crafted by Gen Urobuchi, offering a precursor to the events of Fate/stay night, where survival is far from certain in this brutal game of fate.