Sister Princess

Sister Princess (シスター・プリンセス, Shisutā Purinsesu) began as a series of light novels that ran 54 issues from 1999 to 2003. During this time it was made into a 2001 video game, along with a 13-episode TV anime series that same year which ran 26 episodes from April to October. A manga adaptation also ran June 2001 to July 2002.

A second game was made in 2002 along with a second 13-episode TV series subtitled "Re Pure", a title shared by the third game in 2003.

Plot
Wataru Minakami is a top student who failed his high school entrance exam because of a computer glitch. He later discovered that he was accepted to Stargazer Hill Academy, which is located at a mysterious place called Promised Island. At the request of his father, Wataru is whisked away to the island, and before he can settle in, a dozen of cute and charming girls start to flock him and claim to be his younger sisters. As Wataru gets closer to his newfound siblings, a deeper mystery as to why they were sent to the island comes to play.