Yuzuki is a persocom created by Minoru Kokubunji roughly two years before the start of the series. Yuzuki was created to resemble, physically and mentally, Minoru's late sister, Kaede, who had died from an illness two years earlier. Yuzuki is programmed with all of the data that Minoru could remember about his sister; what she liked, what she disliked, as well as her habits and behaviors. However, Minoru still realizes that no matter how realistic she may be, she is still only a persocom that is following her programming. Yuzuki also possess an awareness of her own limitations.
Toward the end of the anime and manga, Yuzuki loses a large portion of Kaede's personality data as a result of trying to hack into Zima and being counter-hacked by Dita. However, Minoru declines to reenter this data, because he has grown to love Yuzuki for who she is; because she is Yuzuki, rather than because she is a replacement for his sister.