What is "oniai"

, is a Japanese light novel series written by Daisuke Suzuki, with illustrations by Gekka Urū. The series is published by Media Factory and since December 2010 there have been 10 volumes released. There are two manga adaptation series, both serialized in Media Factory's Monthly Comic Alive magazine. An anime adaptation by Silver Link aired in Japan from October 5 to December 21, 2012.