Based on a Japanese mystery light novel series written by Nanako Tsujimura and illustrated by Utako Yukihiro. Shueisha has published eleven main volumes since 2015 under their Shueisha Orange Bunko imprint, as well as two collections of short stories. A manga adaptation with art by Mika Akatsuki has been serialized in Ichijinsha's josei manga magazine Monthly Comic Zero Sum since November 28, 2019.