It was released on January 6, 2021, through Sony Music Entertainment Japan,[2] the same date with their single "Kaibutsu", accompanied the second season of Beastars.

[3] A concept of "reading CD" with binder package, the EP consists of all singles released from 2019 to 2020, including other track "Encore".

[4] The track-by-track cover EP Mikunoyoasobi by Ayase with Vocaloid voicebank Hatsune Miku, was released on the same day exclusively at Tower Records Japan.

[10] For Billboard Japan Hot Albums, The Book entered at number two with 74,601 CD copies, and 10,069 download units.

[11] The Book received a gold certification for both physical and digital release by Recording Industry Association of Japan (RIAJ).