Awakening in a parallel world, Illyasviel von Einzbern is distressed and in trouble, unable to transform and without Miyu Edelfelt or Rin Toosaka for support. The once lively Fuyuki City is in snowy ruins, with a giant crater bored in the middle of the town.

With no signs of people, Illya heads home only to find it in ruins, with no familiar sight of her family. Suddenly, she is jumped on by the mysterious Tanaka, a girl wearing a gym uniform and with no memories. Despite her condition, the cheeky amnesiac offers her help to Illya, and the two take shelter in a playground.

While hiding from the snow, Illya and Tanaka are ambushed by an agent of the Ainsworth family. Though their assailant runs off as soon as they are attacked, it seems more is yet to come in the familiar landscape.