The Holy Grail War. A free-for-all battle to the death between seven pairs of Masters and Servants. Matsushita Ai, at the behest of the organization that has cared for her for ten years, has been sent back to her birthplace to participate in such a clash. Together with her Saber-class Servant, Okita Souji, she will descend into a violent conflict in which there can be one victor.