The series is regarded as being set in an alternate parallel universe to TYPE-MOON's other series, Tsukihime and Fate/stay night, which make references to Kara no Kyoukai. The protagonist of the series, Shiki Ryougi, possesses the same abilities as Tsukihime's protagonist, Shiki Tohno, and Aoko Aozaki's sister Touko Aozaki is a major character. In Fate/stay night, Touko plays a small role in one ending, although she is not directly named.