Acting for Two: In the dub, Mikoto, the Sisters, Last Order, and WORST (and Dolly in Railgun) are all voiced by Brittney Karbowski, while in the original they had a unique actress for each.
Adaptation First: The A Certain Magical Index anime was the first to be localized, released late 2012. The original light novels, however, only started coming out in English in late 2014.
Bob Magruder, the English voice actor of Pope Matthai Reese, passed away on January 2, 2015 due to illness. This was one of his last roles alongside Freezing Vibration as Christopher Mably.
Cole Brown, the English voice actor for Heaven Canceller, passed away while Izetta: The Last Witch was in production for an English release. Bill Brooks take over from Season 3 onwards.
Jim White, the English voice actor of Pope Matthai Reese, passed away on June 12, 2022 from lung cancer.
Development Gag: Ayu Mitsuari's character design was in fact based on a rejected concept art for Misaki. According to Word of God, such rejected designs would be locked away. But since Ayu's role would be of a girl who wanted to be Misaki but failed to do, using an old design for Misaki was fitting.
Executive Meddling: The manga adaptation skipped Deep Blood arc which features Aisa Himegami as the female deuteragonist due to the Editorial Staff wanting to reach the Science Side and Mikoto-focused story arc (namely Sister arc) quickly. Unfortunately, skipping that story arc means sacrificing important character growth for the male lead Touma Kamijou and Adaptation Induced Plothole as well, since Deep Blood arc had never happened in the manga, therefore Himegami's life was never in danger (at least before the Daihasei Festival) and she would have absolutely no reason to transfer school from Kirigaoka Girls Academy (one of the elite schools in Academy City) to Touma's high school (which is just an ordinary school with many Level 0s).
Fandom Nod: The recurring "Headband Girl" Easter Egg is finally acknowledged in-universe in New Testament 13 when High Priest claims the Magic Gods have sent an 'Observer' to track Touma's actions. Touma immediately suspects it to be said girl due to the fact that she always seems to be around him yet he doesn't even know her name (a nod to the popular theory that the Headband Girl is secretly someone important that hadn't been properly introduced yet). High Priest soon after reveals he made this tidbit up.
Marth Debuted in "Smash Bros.": The third season of the series was licensed worldwide by Crunchyroll and Funimationnote North America, Australia, New Zealand, United Kingdom, Ireland, and South Africa, as the previous seasons were never broadcasted in those regions.
The video games, trading card games, the manga adaptation of Miracle of Endymion, and various audio dramas were not released overseas.
The first and second season of the anime series wasn't released in any other country except United States, Canada, United Kingdom and Ireland.
Thankfully averted with the third season that was licensed by Funimation for English-speaking countriesnote North America, Australia, New Zealand, United Kingdom, Ireland, and South Africa and Crunchyroll to be shown for the rest of the world except Asia.
In the English dub, Amanda Lee replaced Krishna Smitha as Itsuwa in Season 3 since the latter is now based in Los Angeles and was not able to record her lines.
Garrett Schenck replaced George Manley as Terra of the Left in Season 3, owning to the latter having personal problems.note These includes having strokes, a heart attack and being homeless while trying to pay half of his bills.
Due to child pornography incident that ended Scott Freeman's career, the role of Pierce Aogami was given to Patrick McAlister.
Pope Reese is now played by Jim White since Bob Magruder passed away in 2015.
Chris Ryan replaced Andrew Chandler as Aqua of the Back in season 3.
Promoted Fanboy: Both Nogi Yasuhito, the artist for Astral Buddy, and Kisaragi Nankyoku, the artist of A Certain Scientific Dark Matter, were fans who were hired as artists of the manga spin-offs for the fanart they had done on the series.
Reality Subtext: In the Index-tan special, Atsushi Abe (as Touma Kamijou) used a voice changer to ask Kaori Kanzaki about her age, her Stripperific outfit, and her voice actress'Lady Drunk antics in the launch of the anime.
Sequel Gap: Season Two of Index finished airing on April 2011 with the third season nowhere in sight until 2018, making a gap of seven years.
The first novel, and consequently the entire series, was originally supposed to be called Last Memory, but the editor had it changed into A Certain Magical Index because the kanji left a strong impression on him when he first read the manuscript.
The 3rd season of Index was originally made to reboot the entire series because it was a long time that nothing related to Index aired after the second season aired.
Word of God: The reason why Stiyl looks so old despite supposedly only 14 was because of a miscommunication between the artist and author: Touma and Stiyl's first confrontation was supposed be something of an Old vs New (which the artist took literally to mean "old man vs. young boy"), completely missing the note that said Stiyl was only 14.
. Unfortunately, skipping that story arc means sacrificing important character growth for the male lead Touma Kamijou and Adaptation Induced Plothole as well, since Deep Blood arc had never happened in the manga, therefore Himegami's life was never in danger (at least before the Daihasei Festival) and she would have absolutely no reason to transfer school from Kirigaoka Girls Academy (one of the elite schools in Academy City) to Touma's high school (which is just an ordinary school with many Level 0s).