Hailing from a prestigious family of magi, Ayaka Sajou is heavily expected to participate in the Holy Grail War. However, following the deaths of her father and sister in the previous conflict, she has become despondent and refuses to engage in the affairs that claimed her loved ones. Soon, she finds herself in serious danger at the hands of a knight, leading her to summon her own Servant, Saber. With him at her side, Ayaka eventually becomes an official participant in the war she had initially sought to avoid.