Oreimo Vol 3 by Tsukasa Fushimi. A Comedy manga rated Teen, published in English by Dark Horse in 2012.

Kyosuke Kosaka has always thought of his younger sister Kirino as a perfect, stuck-up model student. Then he discovers her secret: she's a hardcore otaku, and he's the only one she can turn to for advice. A comedy based on the hit light novel series.