Ore no Imouto ga Konnani Kawaii Wake ga Nai (OreImo) is a comedy light novel by Fushimi Tsukasa. Kousaka Kyousuke, a 17-year-old boy, discovers that his younger sister, Kousaka Kirino, has a secret life as an otaku. He does his best to help her overcome the difficulties her hobbies bring her.
Ore no Imouto ga Konnani Kawaii Wake ga Nai (usually abbreviated "OreImo") is a comedy-genre light novel series by Fushimi Tsukasa. It follows Kousaka Kyousuke, a typical 17-year-old boy, who discovers that his little sister, Kousaka Kirino, has a secret life as a closet otaku. Despite a shaky relationship, he does his best to help her overcome the difficulties her hobbies bring her, including confronting their parents and making new friends.
Included are the original light novels, the 4-volume manga adaptation, both seasons of the anime (the second season is scheduled to begin April 2013), and both visual novels.
For more information, see Wikipedia.