Based on the story serialized in G's Magazine since March 1999, Sister Princess made its way into anime and Playstation game. The story focuses on twelve cute little sisters (Karen, Sakuya, Hinako, Marie, Chikage, Yotsuba, Haruka, Rinrin, Mamoru, Aria, Kaho and Shirayuki) who can’t stop loving their older brother in their own way.
In the anime version, the older brother name is Minakami Wataru. Wataru is a top student at middle school who failed his high school entrance exam. However, he got accepted into Star Gazers Hill West University (high school) by recommendation. Star Gazers Hill West University is located on an island (Promise Island) and he meets two weird people on a boat. One is Yamada Tataru and the other one is Mami.
Just as when he wants to get off from the boat, he falls into the sea and saved by Karen, one of his little sisters. From there and on the story begins...