Abstract: This article examines questions of mediated reality, authenticity, and fandom in the context of two distinct media spaces: Japanese pop idol culture and found footage horror films. These two worlds are linked by the concept of the ‘mutual agreement’ (o-yakusoku)—an agreement between fans and creators that certain illusions of intimacy and reality will not be questioned. In the found footage horror film Shirome, which stars the pop idol group Momoiro Clover Z, we see how this ‘mutual agreement’ serves to empower fans (who can feel a sense of protec- tiveness as the idols they worship are terrorized) and uses the trappings of reality (cheap cam- era work, performers working without a script) to create a fictional world that nonetheless feels authentic to viewers. Ultimately, Shirome is an example of what happens when the insti- tutions of government, family, and religion lose their power and are replaced by transnational, transmedia communities that openly embrace their illusoriness.