Fate/kaleid liner Prisma☆Illya: Vow in the Snow

A young Shirou Emiya and his adoptive father Kiritsugu travel to Fuyuki to investigate rumors about the Sakatsuki family harboring a child with powerful magic abilities. They hope to uncover the truth behind the legends and the potential threat they pose. Their mission sets the stage for the appearance of Miyu and the conflicts to come.

They locate Miyu among the ruins of the city and rescue her. Miyu possesses the power to grant wishes unconditionally, and a mysterious storm seems connected to the thoughts and desires implanted in her by humans. Kiritsugu declares that he will use her power to save humanity.

The Emiyas bring Miyu back to their home. Kiritsugu makes it clear that Miyu should be treated as a tool rather than a person. Shirou begins to bond with Miyu despite the warning, sensing a complicated future.

Kiritsugu dies before he can learn how to use Miyu's powers. His death leaves Shirou and Miyu to navigate a fragile relationship and a looming danger. The family mourns as Miyu's potential power looms over them.

Five years pass, and Shirou lives as a normal high school student with Miyu as his adopted sister. They study alongside Julian and Sakura, hinting at a hidden underworld of magic influencing ordinary lives. The pair navigate daily routines while the threat of Miyu's power lingers.

Shirou decides Miyu should see the world beyond their home. Miyu expresses a simple wish to see the ocean, prompting plans to bring her outside into the wider world. The idea foreshadows the coming conflict between duty and affection.

As Shirou tries to reveal his true intentions, Julian arrives to finish a ritual he started. The vortex consumes Fuyuki, and Shirou is unable to protect Miyu, who is captured by Julian's associates. Shirou is defeated, left for dead while Miyu vanishes.

Shirou regains consciousness under the care of Kirei Kotomine, a local priest. Kirei explains that Julian is from the ancient Ainsworth mage family who intends to seize the Grail to avert humanity's end. Shirou learns the high-stakes nature of the looming Fifth Grail War.

Sakura finds Shirou and offers him a possible path to rescue Miyu, though she would rather he leave the city to stay safe. They are attacked by Shinji, Sakura's elder brother, who wields the Assassin Card. Sakura is killed in the skirmish, and Shirou uses Sakura's Archer Card to empower himself and defeat Shinji, who proves to be Julian's puppet.

Using the Archer Card, Shirou begins hunting down the remaining Servant Card holders, each revealed as Julian's puppets. Kirei congratulates Shirou on supposedly winning the Fifth Grail War and directs him to an ancient cave where Miyu is being held. The march toward the cave marks a turning point in the conflict.

Shirou decides to use his wish to send Miyu to a different world where she can find happiness, even if it defies Kiritsugu's wishes. Angelica, the holder of the real Archer Card, confronts him as the ritual nears completion. Although Shirou is overpowered, he buys enough time for the ritual to finish and Miyu is transported away.

Miyu wakes up in an alternate Fuyuki, now determined to search for the magical cards that grant wishes and shape her fate. She imagines a path forward that diverges from her adoptive family. The ending leaves Miyu resolute on her new journey.