Kyosuke Kosaka, a normal 17-year-old high school student living in Chiba,[4] has not gotten along with his younger sister Kirino in years. For longer than he can remember, Kirino has ignored his comings and goings and looked at him with spurning eyes. It seems as if the relationship between Kyosuke and his sister, now 14, will continue this way forever. One day, however, Kyosuke finds a DVD case of a magical girl anime which had fallen in his house's entranceway. To Kyosuke's surprise, he finds a hidden eroge inside the case and he soon learns that both the DVD and the game belong to Kirino. That night, Kirino brings Kyosuke to her room and reveals herself to be an otaku with an extensive collection of moe anime and younger-sister-themed eroge she has been collecting in secret. Kyosuke quickly becomes Kirino's confidant for her secret hobby. The series then follows Kyosuke's efforts to help his sister to reconcile her personal life with her secret hobbies, while restoring their broken relationship and coming to terms with their true feelings for each other.