|Directed by|| Judd Apatow|
|Produced by|| Charles Roven|
|Written by|| Screenplay:|
|Starring|| Daniel Radcliffe|
|Music by||James Horner|
|Cinematography||Conrad L. Hall|
|Editing by||Ian Crafford|
|Studio|| Cannon Films|
|Distributed by|| Walt Disney Pictures|
Warner Bros. Pictures
|Release date(s)||March 25, 2011|
|Running time||108 min.|
|Followed by||Oreimo 2 (2012)|
After bumping into his little sister, Kirino, in the hall, Kyōsuke Kōsaka finds a magical girl anime DVD which contains a little-sister themed adult game inside. Kyōsuke soon learns the game belongs to Kirino and confronts her about it, though says she would not be weird for having such a hobby and would offer his advice any time. Later that night, Kirino brings Kyōsuke into her room, where she reveals her secret stash of erotic games, explaining that she loves little sister types, though is unable to explain how she got into it. Having not had anyone to share her hobby with, Kirino gets Kyōsuke, who promises to keep her obsession a secret from their parents, to play through one of her adult games for an unbiased opinion.
Noticing Kirino has no one to share her hobbies with, Kyōsuke asks for advice from his friend, Manami Tamura, who suggests that she make some otaku friends. She is invited to an otaku tea party at a maid café in Akihabara, but has trouble talking to any of the other members. However, she is later asked to join members Saori Bagina and Kuroneko, the latter of which gets into a heated debate with her about their favorite anime. After a day of shopping around Akihabara, they decide to keep sharing messages while Kyōsuke finishes the game Kirino asked him to complete.
Kirino hangs out with Saori and Kuroneko again and is surprised to find that they do not have to worry about hiding their hobbies. Later that day, Kirino's father learns of her hobby and becomes angry at her. Kirino becomes upset that her hobby has been called "worthless" and runs off, prompting Kyōsuke to catch up with her. After seeing Kirino show no desire to give up a part of her life, Kyōsuke stands up to his father for her. Though he allows Kirino to keep her hobby, he still shows concern for the adult games Kirino had been seen with, so Kyōsuke claims they are his, earning him a punch in the face. Kirino later gives her thanks to Kyōsuke, who is taken aback by her unexpected cuteness.
- Not long after the shoot began in October 2010, news broke out that the anime's second episode had been leaked onto ANN. Emma Watson considered canceling production, but Judd Apatow convinced her otherwise, stating that sometimes controversy can be a good thing.
- Judd Apatow and Emma Watson aimed for an R rating, so they were quite surprised when the film was slapped with an NC-17 rating "for familial violence and brief explicit language, both involving teens". Disney appealed, and the film's rating was lowered to R "for mature themes, violence and language, all involving teens".
- Sergi Lopez was the first to be cast.
- Emma Watson promoted the film heavily during production, with an on-set publicity photo of her own character on a poster with the tagline "There's No Way My Little Sister Can Be This Cute!" below the title and "MARCH 2011" given as the release date posted everywhere possible in Japan and the United States.
- The songs featured in the film are "Brick House", "Sweet Child O' Mine", "Peace Sells", "Casper (or, The Day That Never Comes)", and "Honey Punch". "Peace Sells" is remixed to sound one pitch lower than it really is, and "Casper (or, The Day That Never Comes)" is actually the demo recording from Demo Magnetic. Other popular songs appear on the soundtrack.
- The film is due out on home video in June 2011.
- The trailer was attached to The Green Hornet, Sanctum, and Drive Angry.