Illya goes to save Shirou, intending to sacrifice herself for him, but he makes the decision to destroy the Greater Grail himself. Desperate for a way for either of them to survive, Illya materializes both their souls, and throws them through the Kaleidescope, into the Illyaverse.
The Chaldea Security Organisation... is not a thing yet, because they never managed to get any funding. So sad. The Wizard Marshal has offered to step in, if they'll give him a hand with these Class Cards that have been popping up all over London. Enter our bold Magical Boy, Fujimaru Ritsuka! His intrepid partner, Mash Kyrielight! And the horrible sticks making their lives hell!
At the moment of transformation, when the connection was to be established and a young girl's life forever changed, the Red Shadow intervened, and the Administration shard became its tool on the path to human salvation. With the power of every hero ever immortalized in myth and legend, what can that girl do but be a hero herself?