The Master of Red Assassin, Shirou was dispatched by the Church as one of the Masters of the Red Faction. He wants to make use of the Holy Grail War to fulfill his own wish. It is unknown if he has any connection to Shirou Emiya of the Fate/stay night timeline. Shirou's true name is Amakusa Shirou Tokisada, the teenage leader of the Shimabara Rebellion. Born in the Edo period, he was a boy of miracles who could nearly be called a saint. However, how exactly he was discovered; a good half of his lifetime is wrapped in mystery. He, who concentrated on his studies since childhood, began to perform many miracles at the frontier for a time. Having healed wounds and walked on water, he eventually began to be enthusiastically worshiped as son of God by the peasants that believed in a prohibited religion. (Source: Type-Moon Wikia)