Waver returns to the Mackenzie household. The old couple, who Waver put under a spell to make them believe he was their grandson, are actually aware he isn't related to them, but enjoyed his and Rider's company. In Caster's lair, Kirei interrogates Iri about Kiritsugu, who he believes is like himself. However, Iri tells him her husband has nothing in common with an empty man like him, as Kiritsugu is fighting for the Grail to wish for a world without conflict. Disappointed, Kirei kills Iri and vows to destroy Kiritsugu's dream. Later that night, Rider and Waver see magical flares sent up the theater, meant to lure them into a duel with Archer. As Rider summons his horse Bucephalus, Waver decides to use all of his Command Seals to give Rider the power he needs to win and conquer the world, as he feels he is no longer worthy of being his Master. Instead, Rider tells Waver he considers him a friend and wants him to ride with him into battle. Kiritsugu and Saber sees the flares as well, aware they are a trap meant to gather the remaining Masters and Servants in the same area. Having sent out the flares, Kirei prepares for his fight with Kiritsugu, sending Berserker to deal with Saber and Archer to face off with Rider. Meanwhile, Iri's soul awakens inside the Holy Grail.

With Kiritsugu and Kirei fighting with all of their skills, Saber finally kills Lancelot where they share one last talk together. As both Kiritsugu and Kirei are about to give each other the finishing blow, a black ooze from the Grail's spreads over them. Kiritsugu finds himself in an illusionary world where the Grail, taking the form of his wife Iri, tells him he is worthy to make a wish for the Grail. However, Kiritsugu is shocked that the Grail is evil when it deconstructs his belief of killing the few for the sakes of many and tells him it cannot save the world and end conflict unless all of humanity must die which it wants to do once it is born onto Earth. The Grail attempts to convince Kiritsugu to make his wish by promising he will be together with his family again by taking the form of both Iri and Ilya. However, Kiritsugu rejects the Grail and kills both his wife and child, as his personal happiness is not worth the cost of the global population. For this, he is cursed by the Grail. Now back in the real world, Kirei scolds Kiritsugu for refusing the Grail and wasting the wish. Kirei pleads Kiritsugu to give the wish to him so that he may find the meaning of his existence, but Kiritsugu kills him without hesitation. Saber soon arrives at the Grail's stage and encounters Archer, who demands that she surrender and devote all of herself to him as his wife. Kiritsugu appears in the middle of their exchange and, to both Saber and Archer's horror, uses both of his remaining Command Seals to force Saber to destroy the Grail using Excalibur.