The series takes place in Fuyuki City in an alternate timeline of Fate/stay night. Kiritsugu and Irisviel helped end the Holy Grail War ritual before it could start, sealing Ilya's memories away and allowing her to grow up as a normal girl. Shirou and Ilya live a peaceful life as brother and sister, without knowledge of magic, under the care of Sella and Leysritt, while their parents are abroad.