Matou Sakura (Sakura Matou in the English release) is an alternate version from her Fate/stay night counterpart that appears in Fate/Extra. She is an NPC character within the Moon Cell's virtual world.
Sakura's light purple hair is very long and reaches to her ankles; she wears a long red ribbon tied on the right side. Beneath a large white lab coat, she wears the traditional school uniform of the Tsukumihara Academy, with a red bow tied around her throat. Her shoes are white, with red toes, and her socks are folded over.
Sakura is very soft spoken and caring; this personality is robotic and repetitive, as she was programmed to follow a specific role by the system of the Moon Cell. However, in certain situations, she can also display strange and out of character behaviors that creep out the Protagonist.
Sakura is first introduced as Shinji's younger sister who works in the nurse's office. As the end of the prologue approaches, Shinji realizes that, while he'd always wanted one, he'd never had a younger sister. Sakura's programming malfunctions during this revelation, exposing her as an NPC programmed to think she is related to Shinji.
During the Holy Grail war, Sakura resumes her position in the nurse's office, handing out weekly supplies to the participants and also tends to any injuries they may suffer during the war that are not a result of "standard" combat; it appears that if she were to leave the office too long, she could lose her job. She is well known for her delicious lunches.
In the upcoming Fate/Extra CCC, she is set to have a vastly expanded role; although, the exact nature of this has not been elaborated on beyond her being the "focus character" of the game.