The manga series adaptation of the Ore no Imouto ga Konna ni Kawaii Wake ga Nai light novels is a series written and illustrated by Sakura Ikeda. The series was first published as a monthly manga series in ASCII Media Works' Dengeki G's Magazine between the March 2009 and May 2011 issues, and was later released in tankoubon format under the same company's Dengeki Comics imprint. Four tankoubon volumes of the manga series were released between October 27, 2009 and April 27, 2011.
The Oreimo manga series follows closely the plot of the light novels, adapting its first two volumes. It focuses on the story of Kyousuke Kousaka, who is not in good terms with his younger sister Kirino, who not only excels in her studies and has many friends, but also has a decent income as a part-time model. In an unexpected turn of events, Kyousuke's normal life is shaken when he discovers Kirino's secret as an otaku, and as a result, ends up taking on the world of an otaku head-on.
The entirety of the manga series has a total of 26 chapters, covering the first two volumes of the light novels and the first five episodes of the first season of the anime series.
- Kyousuke Kousaka (高坂 京介, Kousaka Kyousuke) - a second year high school student and a seemingly "normal" guy with average marks in school and the usual habits of someone his age. His discovery of his younger sister Kirino's hobby as an otaku changes his life as he is forced to experience the life of an otaku for the sake of his sister's secret.
- Kirino Kousaka (高坂 桐乃, Kousaka Kirino) - a first year high school student who is an overachiever in both academics and sports and works as a part-time model in between. Unknown to many, she is an avid fan of eroge that features romantic relationships between siblings and she was the one responsible for his older brother Kyousuke's exposure to otaku culture.
- Kuroneko (黒猫, Kuroneko) - a member of the online group Otaku Girls Unite! and an avid fan of the series Maschera: Lament of a Fallen Beast. She meets fellow member Kirino in an offline meeting and slowly became friends with her, although their personalities often clash with dramatic results.
- Saori Bajeena (沙織・バジーナ, Saori Bajīna) - the moderator of Otaku Girls Unite! and an otaku as well, although she is more inclined to mecha anime. Saori is the one responsible for the meeting of Kirino and Kuroneko, and often ends up mediating when things get heated up between the two.
- Manami Tamura (田村 麻奈実, Tamura Manami) - Kyousuke's childhood friend and the daughter of a family that owns a sweets shop. She is always together with Kyousuke in school, and is known for being just as "normal" as Kyousuke.
- Ayase Aragaki (新垣 あやせ, Aragaki Ayase) - Kirino's friend in school and a fellow part-time model. She does not approve of Kirino's hobby, calling it disgusting, but was able to reconcile with Kirino with Kyousuke's intervention, although at the cost of invoking Ayase's more obsessive side.