The Holy Grail War is a ritual held in Fuyuki City by magi grasping to reach the Root. Seven magi, known as Masters, gather to compete over possession of the Holy Grail, which possesses the power to fulfill any of its bearer's wishes. They fight other Masters for supremacy by summoning Heroic Spirits, known as Servants, called upon by the Holy Grail. However, throughout the past four Holy Grail Wars, history has yet to see a single victor.

During the Fourth Holy Grail War ten years ago, Shirou Emiya was saved from amidst the fires of war by the self-proclaimed mage Kiritsugu Emiya. The young Shirou started living with Kiritsugu and persistently asked for instruction in magecraft, much to the mage's disapproval. On the night prior to Kiritsugu's death, Shirou promised his adoptive father that he'll become a Hero of Justice.

Fast forward to the present. On one quiet eve, Shirou gets involved in the Holy Grail War and is assailed by a Servant. Just as the glint of steel threatens to take his life, a girl clad in knightly armor appears to stop the fatal attack. The Servant, who came to the rescue of the would-be Hero of Justice, and the Master, saved by the Heroic Spirit of the Sword; their fates are in motion...