In Chobits manga and anime, Kaede Saito is the sister of Minoru Kokubunji. How can she be the brother of Minoru Kokunbunji, when her last name is different than those of her brother's?
Their parents are divorced. Thus, they have different last names. This proof is further noticed in an episode of Angelic Layer anime; after Hikaru angel and Blanche angel duel ends, she states that she does not have a mother. To further elaborate, it is interpreted that she lives with her father while her brother lives with his mother. Therefore, she no longer has a mother AT HOME. You will probably realize that in one of the episodes of Angelic Layer anime, another woman is with her father at home. But, you never hear Kaede say okaa-san (mother) to that woman.
Unfortunately, in Chobits manga and anime, she dies of an illness. Minoru, who could not accept the fact that his sister died, created a persocom by the name of Yuzuki. Minoru inputs in programmings into Yuzuki that best represents his lovely sister's appearance and characteristics. Minoru states that seeing Yuzuki makes him sad and happy at the same time because he can live in a dream where his sister is still alive However, the painful reality is Yuzuki is not his sister. Later on, Minoru slowly realizes that Yuzuki could never be the replacement for his sister and that Yuzuki could not be replaced as well. Thus, he stopped inputting data into Yuzuki knowing that inputting the data is meaningless.