On a quiet evening, an enchanted magical wand called Ruby visits a surprised young Illyasviel von Einzbern. On the run from her abusive owner, Ruby quickly senses great magical energy in Illyasviel and transforms her into a magical girl. Blessed with extraordinary and unique powers, she now assumes the identity of Prisma Illya.

But Ruby's previous owner demands Illya's services, for her hometown Fuyuki City is in peril. Dispersed throughout the city are the Seven Class Cards. Rife with magical energy, these Class Cards pose a threat to the stability of the quiet town, should they fall into the wrong hands.

As a magical-girl anime addict, it seems Illya is duly suited for the job. But as she enlists the aid of both fellow primary schoolers and top-ranking Magi, this mission may turn out to be more than she bargained for.