Ore no Imouto ga Konnani Kawaii Wake ga Nai

Synopsis

After Kirino gets annoyed with her for not understanding certain aspects of her hobby, Ayase asks Kyosuke to give her advice on a present she can give her to make up with her. After shopping around with Kuroneko and Saori for ideas, Kyosuke learns of a cosplay contest offering a rare Meruru figurine for the winner. With Ayase objecting to cosplaying, they manage to trick her model friend, Kanako Kurusu, into cosplaying as Meruru for the contest. However, when they spot Kirino in the audience, Kyosuke has to make sure Kanako does not spot her. Kanako manages to put on a winning performance and win the prize and, despite the disgust she felt towards the otaku fans, admits that she had fun while doing it.

(Source: Wikipedia)