Yamato Nagamori is the central figure in Lucky Star: Ryōō Gakuen Ōtōsai, a PlayStation 2 game based on Lucky Star. She arrives as an enigmatic transfer student alongside the protagonist. Previously enrolled at Saint Fiorina All-Girls High School and part of class 2-3, she moves to class 3-B, the same class as Konata. Yamato displays a cold, spoiled, and mysterious demeanor, embodying a typical tsuntsun personality. During her junior-high days, she was close friends with Kō. Her interests include karaoke and cycling, while her favorites are soft azuki bean jelly, Yukimi Daifuku, and summer. Conversely, she dislikes shellfish and winter.
Prior to the game's timeline, Yamato was involved in a spaceship accident during Ryōō's school festival. To prevent this catastrophe and save Yamato's life, an alien aboard the spaceship merges with her and reverses time several days before the festival. The alien then informs the protagonist about the reasons behind the time loop and reversal, hoping they can identify and eliminate potential triggers for the spaceship disaster using their déjà-vu experiences. After successfully erasing these events, Yamato reveals her true identity as an alien, leaves her host body, and wipes everyone's memories of the incident. It is assumed that Yamato resumes her original identity and returns to Saint Fiorina All-Girls High School.
