Ore no Imouto ga Konnani Kawaii Wake ga Nai.

Synopsis

Kirino reminisces on her childhood, when she was very fond of Kyosuke and always looked up to him, until he stopped giving his all and adopted a more relaxed lifestyle. Blaming Manami for the sudden change in him, Kirino confronted her, asking her to give back the brother she loved so much, just to hear from her that the Kyosuke she envisioned never existed in the first place. To get back at Kyosuke, Kirino focused to improve herself and started avoiding him. Years later, she starts working as a model and befriends Ayase, but also develops her otaku hobbies, and becomes too ashamed to share them with anyone else. The issues she had with her secret were what somehow reapproached her with Kyosuke, who since then always stood by Kirino's side to support and protect her, even though she no longer sees him as the brother she once idolized.

(Source: Wikipedia)