Naomi Saeki attends Homurahara Academy as a second-year student in Class 2-D. A member of the track and field club, she is considered one of its promising athletes. She has an older brother. Naomi possesses a caring personality, often acting with consideration for others and accommodating the eccentric ideas of her classmate, Kaede Makidera. Her philosophy for strengthening the track club focuses on making it "bright and fun," contrasting Makidera's rigorous Spartan approach. Her personal interests encompass card games, board games, and tabletop role-playing games (TRPGs).

Within the context of the special, Naomi becomes the Master of the Caster-class Servant, Leo III, during the Holy Grail War narrative conceived by their classmate Yukika Saegusa. Leo III employs a tube-like apparatus to launch rockets, emit fire, and achieve propulsive flight. During this story, her Servant defeats the Lancer and Rider-class Servants, battles Saber, and is ultimately forcibly displaced by the Servant Plato.

Naomi Saeki, alongside Makidera and Saegusa, is portrayed as an ordinary high school student without magical abilities or awareness of Fuyuki City's supernatural occurrences. Her daily life centers on typical school activities, maintaining a peaceful existence distinct from the larger Fate universe events. Her involvement in the Holy Grail War occurs solely within the fictional narrative framework of the special.