Illyasviel von Einzbern is an ordinary elementary school student who becomes a magical girl when the magical Kaleidostick Ruby deems her a more suitable master than the sorceress, Rin Tohsaka. Rin, who had been tasked by the wizard Zelretch to collect the seven Class Cards containing the spirits of Heroic Spirits from legend, finds that she is unable to change Ruby’s mind and must supervise Illya in completing the task of collecting the Class Cards. During Illya’s adventures, she receives a friend and rival in a girl named Miyu, the contracted master of the Kaleidostick Sapphire, which similarly abandoned its original master and Rin’s rival, Luvia Edelfelt.
After a series of battles, Illya and Miyu were able to collect all Cards and became good friends, while Rin and Luvia remained in Japan by the order of Zelretch. However, the appearance of Kuro, a dark-skinned girl with a striking resemblance to Illya, soon complicates their lives as she attempts to eliminate Illya. Their battle is interrupted by the arrival of Illya’s mother, Irisviel, who reveals that Kuro was originally intended to be the Holy Grail in the Holy Grail War, but after the war was prevented Kuro was sealed away so Illya could live a normal life. Illya supplies Kuro with the mana needed to sustain her physical form, and accepts her into the Einzbern family.