The fate of humanity hangs in the balance, as the Ainsworth family possesses the Holy Grail – the only hope for survival in a world on the verge of collapse. Yet, to activate its power, they must offer up Miyu, a young magical girl. Despite the danger, Shirou refuses to let his sister be sacrificed and vows to protect her. It's now up to Illya to find a solution that will save Miyu and the world from certain destruction. However, the cost of saving everyone is the life of one innocent girl, leaving Illya with a tough choice to make.