A behind-the-scenes look at the long development of The Sekimeiya: Spun Glass which began in early 2016, written by the three main developers of the project and a special guest author. The 47 page development book includes sketches, proofs of concept, old art pieces, exclusive material, and tons of details about the journey. Once you've finished the game, a new option will appear in the main menu to view the development book in-game. You will also receive it as a PDF document in the game folder.

In the event the development book button doesn't appear in the main menu, search jump to the last line of the game and skip to the end to unlock it.

Also included is a 7z archive containing all the CGs and cover art in their original resolution in PNG format, as well as some PSD files.

Originally a Kickstarter reward, the development book was made available to the general public on August 3rd, three months after the game's release.