Kirino is Kyosuke's 14-year-old younger sister. She is normally mature and independent for her age in front of others, but her true personality is at times immature, abusive and ungrateful with an aggressive, tsundere-like personality. Mostly only to Kyosuke does Kirino show her much more intolerable personality, where she orders him to play her games and care for the characters, only to insist that 2D and 3D worlds should be kept separate and accuse him of being a pervert and a lolicon afterwards.

She is secretly an otaku with an obsession for "little sister"-themed eroge, as well as the children's anime series Stardust Witch Meruru. She works as a magazine model and later becomes a novelist, the funds from which she uses to support her hobby. Despite her interests, she states she does not know why she started liking eroge and denies having a brother complex. Nevertheless, she frequently forces Kyosuke to spend time with her, whether it is playing games or taking her out, but denies that she actually enjoys the time they spend together.

Oreimo, short for Ore no Imōto ga Konna ni Kawaii Wake ga Nai (俺の妹がこんなに可愛いわけがない, lit. My Little Sister Can't Be This Cute) and also known as Ore no Imōto (俺の妹?), is a Japanese light novel series written by Tsukasa Fushimi, with illustrations provided by Hiro Kanzaki. The series includes 12 novels released between August 2008 and June 2013. A manga adaptation drawn by Sakura Ikeda was serialized in ASCII Media Works' Dengeki G's Magazine. A 12-episode anime adaptation produced by AIC aired in Japan between October and December 2010.

Four additional episodes, which offer a different ending to the broadcast series, were streamed monthly via the official website and other video streaming sites between February and May 2011, before being released on Blu-ray Disc and DVD in June and July 2011. A 13-episode second anime season produced by A-1 Pictures, titled Ore no Imōto ga Konna ni Kawaii Wake ga Nai. (with a period at the end), aired between April and June 2013. An additional three episodes were streamed online on August 18, 2013.