During a peaceful summer, Illyasviel von Einzbern, taking a break from her magical girl duties, enjoys leisure time with her friend Miyu Edelfelt after their Class Cards adventure. However, their tranquility shatters when Rin Toosaka and Luviagelita Edelfelt abduct them. Informed by Clock Tower that unsealed mana threatens Fuyuki City, the magical duo must confront the lingering chaos. Tasked with resolving the anomaly's source, Illya and Miyu cast a spell only to witness Illyasviel split into two! As her enigmatic doppelgänger flees, Illya ponders the repercussions of this unexpected turn of events.