Ore no Imouto
Ore no Imouto hentai (My Little Sister Can’t Be This Cute) also known as Oreimo.
Ore no Imouto ga Konna ni Kawaii Wake ga Nai is Japanese light novel with anime and manga adaptation.
Its about Kyousuke Kousaka, a normal 17-year-old high school student, and his younger sister Kirino. They are not getting along at all, she ignores him at any occasion, until he finds out about her secret. Secret that noone knows about, even her best friends. She is otaku with extensive collection of moe anime and younger sister-themed eroge, that she has been collecting in secret. Kyosuke becomes Kirino’s confidant for her secret hobby.