Ore no Imouto ga Konnani Kawaii Wake ga Nai (a.k.a My Little Sister Can't be this Cute) was originally small novel written by Tsukasa Fushimi but was then adapted into a manga and then into an anime.

Plot:

Kyosuke Kosaka is a normal seventeen year old, whose family is a bit odd. Kyosuke is constantly being over shadowed be his fourteen year old sister, Kirino. There is also the fact that there relationship is quite distant, to the point where Kyosuke can't even remember the last time that he has had a conversation with his sister. His mother and father are polar opposites; the father is a strict police officer, while the mother is a relaxed woman. Well one day Kyosuke finds an anime case at the front door, but inside is an adult game titled "Make Love With Little Sister". Knowing that the disk belonged to someone in the house Kyosuke decides to investigate, because if the disk were found it would automatically be assumed that it was his. So at dinner Kyosuke casually mentions the anime from the case that the game was in, in order to set the trap. Later that evening Kyosuke finds Kirino searching his room. After he shows her the case and she denies knowledge Kyosuke just asks her to throw it out then, and that would be the end of it. But later that night Kirino slaps Kyosuke awake and tells him to come to her room, there she comes out as an otaku and shows him her impressive collection of little sister adult games. From there Kyosuke is enlisted to help hide Kirino's "hobby" from their family and friends, as well help her find more otaku friends.

Review:

This series is better than it has any right to be. Like many people I scoffed at it because of the premise and the creeper factor. True, it has a rating of 4.5 out of 10 on the creeper factor, but it actually is quite decent, all things considered. I especially enjoyed the anime version, if not just because of an art style that gets used a little to often in the manga and the name is escaping me but I will post an example at the end of this. Also the anime is fairly consistent with the manga which is big ups in my book, I can't speak to the light novel because I haven't read it. The series definitely has it's comedy moments that aren't just chuckles. But it also has it's serious moments as well, especially when it comes to stereotypes of "otakus" and the stigma that that creates. It really does speak to the authors view point, that just because a person likes a certain thing doesn't mean a person will become a criminal. But one of the things that American audiences might not be able to get around is the little sister adult games. Because laws are different regarding such things in Japan than the US it might be a hard sell. Still this was a pleasant surprise and I would recommend looking for the anime since that just recently ended.

Here is an example of the art I was describing in the last four panels.