Sister Princess is a popular Japanese seinen series written by Sakurako Kimino and illustrated by Naoto Tenhiro. It began as a serialized light novel series in 1999.
In 2001, a manga series and a bish?jo game for the Sony PlayStation were released. Sequels to the game were released for the PlayStation and Game Boy Advance. Sister Princess was also adapted into a Japanese anime television series.
In the anime, Chikage claims that she and the brother have been together in previous lives, possibly as brother and sister, perhaps as lovers.
She expresses a desire to have him for herself somehow, but admits that he has refused the offer or simply slipped from her grasp several times throughout their incarnations.
Out of all the sisters, she is the only one who entertains thoughts of somehow taking the brother away from the others, and almost executes plans to do so.