Oreimo

俺の妹がこんなに可愛いわけがない

Kyousuke Kousaka, an unremarkable high school student, discovers that his overachieving younger sister Kirino has been hiding a massive collection of moe anime and little-sister-themed eroge. Kirino, who projects a perfect-student image at school, reluctantly drafts Kyousuke as her confidant and guide through the otaku world — from late-night online communities to Akihabara shopping runs. Their strained sibling relationship shifts as Kyousuke is pulled deeper into the hobby Kirino cannot share with anyone else.