The two novella-length offerings were originally included as bonus features in the initial Japanese Blu-ray releases, while the introduction and the titular story are unique to the book. A manga rendering of this official spinoff is slated to appear stateside from Kodansha Comics.
The writer of many of the episodes of the smash hit animated series Attack on Titan, Hiroshi Seko has served as the scenarist for the small-screen adaptations of other popular franchises such as Seraph of the End and Ajin: Demi-Human.