Sister Princess (Japanese: シスター・プリンセス, Hepburn: Shisutā Purinsesu) is a Japanese light novel series written by Sakurako Kimino and illustrated by Naoto Tenhiro that began serialization in 1999 and ended in 2003. In 2001, a manga series and a bishōjo game for the PlayStation were released. Sequels to the game were released for the PlayStation and Game Boy Advance.

Sister Princess was also adapted into two anime television series, both broadcast on TV Tokyo. The first series was produced in 2001 for 26 episodes. The second, Sister Princess: RePure, aired 13 episodes in 2002.

The premise behind Sister Princess is that an ordinary young man (the player) is made to live with twelve lovable little sisters, each with their own distinct quirks and personalities. The game itself plays out like a dating sim. Players have about a month to spend with the sisters with each day broken up into three segments: first is the free time period before noon, followed by the period after lunch and ending with another period of time before bed. During day time, the player can choose which of the girls he wishes to escort to school, if any. The period after lunch is similar to the one in the morning, with additional choices which allow the player to go to various places in town besides walking home with one of the girls. Every night before bed, the player will be allowed to check his e-mail and send replies. As the player continues to interact with the sisters, their reactions to their big brother will change accordingly until the ending.

There are two different endings for each sister: the normal ending and the "non-blood relation" ending. As the name would suggest, the special ending reveals that the brother-character and sister are not actually related by blood. In the case of some of the older sisters, this can lead to the protagonist and "sister" marrying one another. In the original Sister Princess, the player can see two different endings for each sister, but Sister Princess 2 has four endings for each sister. The first two were the non-sibling relation and siblings-together ending and, if the player chooses one sister in the beginning but ends up with another sister, either of the other two endings for the first sister who the player does not choose appear ("non-blood relation" ending and "still brother and sister forever" ending also) but with a different story.

For Sister Princess 2, the story begins on the final day of school before summer vacation. Then the player chooses a sister who he wants to start with for a close relationship. Therefore, Sister Princess 2 is about spending the player's time with either one sister or all sisters at the same time as they spend their summer together. Especially in Sister Princess 2, the player can spend the summer with all the sisters, not just one, in a special ending where the sisters invite their brother to a summer party where the brother and the sisters would swear to be together forever.

He later chooses Karen as his soulmate and "The Promised and only Dream Girl".

Each sister has a unique method of addressing her older brother. Each method is derived from either onii-san or ani, both of which mean "older brother". However, most of the methods are rarely or never used in Japanese culture, except for Karen's onii-chan and Rinrin's aniki. There is never any sibling rivalry among the sisters: although they certainly each vie for his time and attention, they never see themselves as competitors; their unconditional love for him only strengthens their bonds with one another. The sisters not only regularly hang out with one another (often to exchange tales of how wonderful a brother he is), but they also arrange to "share" him when he inadvertently neglects to or cannot regularly visit any of them.

She is later revealed as Honda Karen.