Kazuma Miki, the light novel editor, apologized to fans who attended the Dengeki Bunko Autumn Festival 2015 in October for not having a sequel to A Certain Magical Index II (2010) "yet".

[49] In June 2018, J.C.Staff was confirmed to be producing the series, while Hiroshi Nishikiori and Yuichi Tanaka returned from the previous two seasons as the director and character animation designer, respectively.

Hiroyuki Yoshino, who scripted A Certain Magical Index: The Movie – The Miracle of Endymion (2013), was confirmed to be the series composition writer, replacing Masanao Akahoshi.

Miki said that the production committee decided in the end to adapt the remaining volumes for the new season since fans wanted the whole story to be completed.

[49] In June 2018, Rina Satō, Nobuhiko Okamoto, and Satoshi Hino were confirmed to be returning as Mikoto Misaka, Accelerator, and Shiage Hamazura, respectively.

[50] Additional cast members were announced in September 2018, including Yoko Soumi as Elizard, Kei Shindou as Carissa, Sayaka Harada as Villian, Takehito Koyasu as the Knight Leader, and Toshiyuki Morikawa as Fiamma of the Right.

[81] The series received heavy criticism from fans due to its "paltry" run and "wonky pacing", prompting them to send Nishikiori their hate messages.