Despite his adoptive father's cautionary advice, Shirou Emiya develops a close familial relationship with Miyu, a girl discovered in the rubble of a once-thriving metropolis. However, as Miyu integrates into mainstream school, the Ainsworth family and their operatives exploit the opportunity by abducting her with intentions of a sinister sacrifice. Faced with the enormous power and potency of Miyu's abilities, both positive and negative, Shirou must act promptly to rescue his sister and eradicate the danger that her capabilities pose.