Fate/kaleid liner Prisma Illya - Season 4 Episode 9 Illya's Choice

Angelica further explains the situation that because the world's decreasing mana is killing off lifeforms, the Ainsworths intend to use the Holy Grail to change humanity into a species that can survive in this new environment. Forced to use the Assassin Card to escape, Illya, conflicted over choosing between Miyu and humanity, is rescued by Kuro, who states her determination to save Miyu regardless of the situation. As Darius forces Miyu to watch everyone's battle, Illya comes to her own decision, stating her determination to save both Miyu and the world without sacrificing either.