Fuyuki City's 5th Holy Grail War was underway. Ten years ago Kotomine Kirei and Emiya Kiritsugu battled during the 4th Holy Grail War, which lead to a fire. Kiritsugu, after assumedly defeating Kotomine Kirei, saved a boy from that fire. However, Kirei still lived and adopted that boy as his own. As such the boy grew up as Kotomine Shirou. The Holy Church had a very obvious advantage in the war as Kirei, Shirou, and the girl that Kotomine Kirei was caring for and teaching (Rin), were all masters in the grail war. As far as Kotomine Shirou could tell, all was going right in the plan to save the world from the Grail falling into the wrong hands, but there's a great deal in Kotomine Shirou's life that he's been blinded to.