Despite his adoptive father's warnings that the girl found in the remnants of a destroyed city is too dangerous to be considered anything other than a tool or weapon, Shirou Emiya comes to treat Miyu as a younger sister. But when Shirou relaxes his guard and Miyu starts normal school, the Ainsworth family and their agents swoop in, kidnapping the girl with the goal of sacrificing her! Faced with the realization that Miyu's ability to do good will always be equaled by her capacity for destruction, Shirou must attempt to both rescue his adopted sister, and decide how to confront the threat that her powers will always pose.

From a surreal talk show where a berserker hostess puts her hapless assassin brother co-host through an increasingly grueling wringer, to spicy ramen endurance tests, magical girls gone wild and wholesale gender-swapping for no apparent reason, you've never seen anything like Fate/kaleid liner Prisma☆Illya: Prisma☆Phantasm

The world is dying, no longer able to support life. The Ainsworth family can use the Holy Grail to save humanity, but the price of salvation is sacrifice of the magical girl Miyu — but Miyu’s brother, Shirou, won’t let them have her without a fight. Now it’s up to Illya to step in and find a solution that will save not only Miyu, but the entire world for impending doom. But when the price for the world's salvation is the life of a single, innocent girl, what will Illya choose?