The Book (本, Hon?) is a supernatural book desired by different parties of ability users. It is said that anything written in the book becomes a reality. Its whereabouts are unknown, however many say it is sealed.
The Book's true appearance and whereabouts are unknown. However, it is said that its pages are all blank.
Very little is known of the Book. It's rumored that it was part of an unknown ability user's power.
The Book has yet to be seen. Fitzgerald mentions it to Atsushi Nakajima, whom he claims is the 'guidepost' to the book itself, as it is located in Yokohama. Fitzgerald intends to use the Book's power to revive his deceased daughter, in hopes of improving Zelda's mental state and restore his family.
Fyodor desires the Book as well. He intends to use it to eliminate ability users as a whole, however why he wants to do so is unknown.
The Decay of Angels succeeded in stealing a page from the Book from Chief Taneda. With it, they wrote a scenario to frame the Armed Detective Agency for a large hostage-murder situation, resulting in Nikolai Gogol's apparent death and the ADA as scapegoats for the attack. This is the first time the Book's power is confirmed true.
The Book is full of blank pages, all able to alter reality even if torn out of the Book itself. However, it has some restrictions, likely implemented by its former user:
- Only a few sentences can be written on each page.
- As a story, the Book's contents must follow rules of karma. This means that extreme statements, such as "All of humanity will be destroyed", cannot be brought to reality.
- What is written in the Book or page must follow a narrative of a story. In accordance with restriction number 2, anyone using the page must make a number of events occur with their own efforts in order to follow the flow of the narrative. Only then would certain desired events written in the Book or page become reality.
The Book acts as a "melting point" or "center" of multiple universes.
The Book's effect on BEAST's Osamu Dazai is minimized. Thanks to No Longer Human, Dazai is largely affected by the memories of himself in different universes, giving him an overwhelming amount of knowledge on the variants of different events.
Although the main events are referred to as the "root universe", this does not make it the "original universe", as the book allows all universes to coexist and separate. "Root universe" is used in order to avoid confusion.