Fate/kaleid liner PRISMA ILLYA - The vow in the snow
After discovering her in the remnants of a destroyed city, Shiro Emiya comes to treat the dangerously powered Miyu as a younger sister. But when Shiro relaxes his guard, the Ainsworth family swoops in, kidnapping the girl with the goal of sacrificing her! Faced with the realization that Miyu's ability to do good will always equal her capacity for destruction, Shiro must attempt to both rescue his adopted sister, and decide how to confront the threat that her powers will always pose.