As a character of the original novel series since Volume 6, Nanaha is Taro Sado's cousin. She is a junior high school student and sometimes visits Taro's room, making Shizuka and Tomoko angry. Although first cousins can marry under the family law in Japan, however, Taro is not sexually attracted to Nanaha because he feels that she is a member of his family. Nanaha is hated by Shizuka and Tomoko, and they treat her very badly.

(Source: Wikipedia)