Another pleasant summer passes for Illyasviel von Einzbern. Stepping away from her magical‑girl responsibilities, she relishes a pause after gathering the Class Cards alongside her closest companion Miyu Edelfelt.
Yet that respite ends abruptly when Rin Toosaka and Luviagelita Edelfelt seize both girls while they are out with friends. The duo learns their mission is far from finished, as the Clock Tower reports that the uncontrolled mana—supposedly sealed—continues to spread across Fuyuki City. Heading toward the source, Illya and Miyu are charged with fixing the disturbance.
But once they unleash their incantation, Illyasviel realizes she has divided into two beings! Watching the enigmatic duplicate dart away, she can only speculate: what will unfold with her doppelgänger roaming the unsuspecting streets? She attempts to pursue it, yet it slips through alleys and vanishes into a market stall. The city"s residents remain oblivious, while Illya questions whether this new entity will cause havoc or help her. Meanwhile, the Clock Tower"s alarm continues to echo, urging them to act.