Based on a light novel series of the same name by Fushimi Tsukasa, illustrated by Kanzaki Hiro.

Kousaka Kyousuke, a normal seventeen-year-old high school student, had not gotten along with his fourteen-year-old sister, Kirino, in years. For longer than he could remember, Kirino had ignored him entirely and even abused him. It seemed their relationship would continue that way forever.

However, one day he found out that Kirino was secretly addicted to anime, manga and visual novels, including adult games, and had a gigantic collection of them all. Having discovered her secret, he was forced into a long chain of events that included helping hide it all, but would lead him to help her learn to deal with her hobby in a better way, including eventually finding real-life friends with similar tastes, and with whom he, too, would get acquainted. Several months passed.

The time spent so far may be fairly long time for their ages, but still little has changed. Kirino is still less than nice to her brother, her inability to deal with her hobby properly has not quite subsided, and she is still very passionate about her favourite anime, Hoshikuzu Witch Meruru (Stardust Witch Meruru), and her adult games. While now Kyousuke has means of reaching some of her friends, a few of whom are also his friends, her behaviour still forces him into dealing with a lot of unexpected trouble. Meanwhile, it could be said that, among her friends, there are one or two who might be interested in being more than just friends with him... Or could it?