Prequel to Fate/Prototype.
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Young Ayaka Sajyou wakes up to a normal morning breakfast with her father and older sister, Manaka, unaware that a battle of frightening proportions has now begun in Tokyo. This battle is the Holy Grail War, the first of a series of mutual slaughters where seven Magi and seven Servants team up together to fight in a battle royale to win the Holy Grail, a mystical omnipotent wish-granting device to have their own wishes granted.
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As each of the Seven Masters summon their Servants and fight, more of the mysteries surrounding the Holy Grail are revealed, culminating in a epic battle that will test loyalties, forge new alliances, and makes one question, who is the real Master in this Holy Grail War?