History YMMV / ACertainMagicalIndex

** In the Side Story, ''Biohacker'', Touma and Seria are hit at one point by a plague of rats carrying a modified disease designed by the eponymous Biohacker that leaves them paralysed. They're able to recover, and Touma notes that things could have been a lot worse if the disease was modified from something deadly like [[https://en.wikipedia.org/wiki/Ebola the Ebola virus]] or [[https://en.wikipedia.org/wiki/SARS-related_coronavirus the SARS coronavirus]]. [[UsefulNotes/COVID19Pandemic Yeah...]]

* FandomSpecificPlot: Many ''Literature/ACertainMagicalIndex'' fans agree that [[EnsembleDarkhorse Frenda]] [[KickChick Seivelun]] from ITEM was underutilised, underdeveloped, and killed off in an undeserving manner. Some fans actually went out of their way to make FixFic where she survives for much longer and legitimately contributes to the plot, usually by forming a duo with the local TeamNormal Saten.

** Mikoto can be shipped with practically anyone from Science Side regardless of their gender. Other than mainstream pairing Mikoto/Touma and Mikoto/Kuroko, [[FoeYayShipping Misaki Shokuhou and Accelerator often get paired with the aforementioned Electromaster]]. Oh and let's not forget that Mikoto/[[TeamNormal Saten]] has a rather small but solid fanbase too.

*** [[TheHero Touma]] and [[TeamNormal Saten]] get paired in a surprising amount of fanfics, despite the fact that they've only met face-to-face when he borrowed her good luck charm for the Daihasei Borrowing Race. Probably because they're both normal (mostly) and that Saten's protection charm actually managed to negate Touma's bad luck for once.

* SignatureSeriesArc: The Sisters arc, both versions of it, is generally considered the most memorable and liked arc in the franchise. Or at least it used to be the case: the Magic God Othinus arc, most especially [=NT=] Volume 9, has become just as popular among novel readers, and is either considered a strong second contender to the title behind Sisters, if not even seen as surpassing it in the the opinion of some.
* SignatureScene: A popularity poll ran for the best scenes in the franchise, with the results featured in the mobile game Imaginary Fest's second anniversary. The winning scene was Touma's PreAsskickingOneLiner "Grit your teeth, weakest" as he punches out the top esper Accelerator to put an end to his massacre of the Sisters.

** Exclusive to fan-translations of the Light Novels is the changes to the names of the religious denominations that the Magic side belong to. They're clearly based on real life church denominations, but the original script (as well as official translations) use Japanese slang terms to refer to them (e.g. "Crossism" instead of Christianity, "Roman Orthodox Church" instead of the Catholic Church, etc.). Fan-translations will forego the slang and just use the real life names instead, and is almost universally accepted in the fandom as the "correct" terminology.

** "KnT", which is short for [[spoiler: "Kamijou no Touma", to refer to Touma's EnemyWithout]] that appears in New Testament 22 Reverse.

** "Headband Girl" for the currently [[NoNameGiven unnamed girl]] that appears in the background of various light novel illustrations. The Illustrator apparently refers to her as "mob-ko" ("background girl"). [[spoiler: She is also sometimes called "Observer-chan" after the reference made towards her between High Priest and Touma in NT13]]

* ArchivePanic: Since the series' start back in 2004, it just ''hasn't stopped''. The Old Testament consists of 24 novels (including two series-relevant side stories), New Testament consists of 23, and Genesis Testament is likely to reach that number of volumes too. Most novels average between 300-400 pages, and yes, you ''will'' need to read all of them in order to avoid ContinuityLockout.

** While not calling her by her InSeriesNickname "Biri Biri," fans also call Mikoto [[Franchise/{{Pokemon}} pikachu-tan (pikachu-chan) or pika-pika-tan.]]

** '''''Pendex''''' for Index's Johann's Pen Mode.

* EnsembleDarkhorse: Now with the second season of Index, Fukiyose Seiri has become very popular with fans on her debut in Episode 8. Her AdaptationalCurves in the anime compared to how she appeared in the novels certainly helped.

** It's also fairly common fanon that Laura Stuart is Index's mother, especially since the two are specifically drawn to resemble each other. This also adds an extra KickTheDog element to Laura's treatment of Index if you buy that theory. [[spoiler:This was disproven by the revelation that Laura is a demon.]]

* SeinfeldIsUnfunny: ''Index'' provides one of the earliest examples, and one of the major {{Trope Codifier}}s, of the StockLightNovelHero archetype. Because of this, many people trying to get into the series now (after the genre has become one of the most saturated in the medium) find it hard to see past its generic over-powered hero, the bevy of beautiful girls vying for his attention, or its ExtranormalInstitute setting. However, being from a time ''before'' those formulas became standardized, it also has many elements of a {{Shonen}} series, as well as a greater emphasis on WorldBuilding and extremely entertaining fight scenes, which people who dismiss it at-a-glance may miss out on.

** It's also fairly common fanon that Lola Stuart is Index's mother, especially since the two are specifically drawn to resemble each other. This also adds an extra KickTheDog element to Lola's treatment of Index if you buy that theory. [[spoiler:This was disproven by the revelation that Lola is a demon.]]
** Fans have theorized for years that Aogami Pierce is the 6th Level 5, by this point they would be furious if it turned out it wasn't him.

* EnsembleDarkhorse: Now with the second season of Index, Fukiyose Seiri has become very popular with fans on her debut in Episode 8. Her anime AdaptationalCurves compared to how she appeared in the novels certainly helped.

* EnsembleDarkhorse: Now with the second season of Index, Fukiyose Seiri has become very popular with fans on her debut in Episode 8.

** There's also a minor one with Touma and [[spoiler:Mitsuko]] versus [[AnythingThatMoves Aogami]] and [[spoiler:Mitsuko]].

** Kuroko swapping minds with a president in Angel Fall becomes this after her English voice actor Creator/AlisonViktorin lost her job after a couple of political related tweets.

** Aogami's [[AnythingThatMoves perverted tendencies]] seem less funny when his English voice actor, Creator/ScottFreeman, was arrested and convicted of possession of child pornography.

* TheChrisCarterEffect: A frequent phenomenon among fans. The [[LightNovel/ACertainMagicalIndex series]] has by now introduced so many plot-relevant characters with [[AlwaysABiggerFish even more potent powers]] with their own storylines that many people have trouble keeping up even with character charts. Combine this with the fact that the revelations about Imagine Breaker and the way Espers work have been minimal so far (and many other less important questions haven't been answered either, but [[KudzuPlot rather just raise new questions]]) and that CharacterDevelopment has been all but non-existent for the majority of characters as of late (including main character Touma), and that the staff seems to be more interested in working on the spin-offs rather than the main story, and you have a giant chaos that has little potential of eventually wrapping itself up completely.

** Not to be left out, the third main character Shiage Hamazura. There are those who like him for being a true Level 0 unlike Touma [[BadassNormal who still kicks ass with nothing but wits, guns, and luck]] [[spoiler:(even defeating his own Level 5 Mugino)]], which makes him something of an AudienceSurrogate like [[Manga/ACertainScientificRailgun Saten]], and they think his relationship with Rikou is very sweet while being amused by his ButtMonkey status in ITEM before (slowly) gaining more respect from them. There's also the fact [[spoiler:he's the first person to truly inconvenience Aleister]]. On the other hand, there are those who dislike him because he's not that attractive compared to Touma or [[spoiler:Accelerator]], he doesn't have any cool or interesting powers unlike the rest of the main characters yet manages to pull out wins against incredibly dangerous enemies due to the story seemingly bending over backwards to give his foes the Idiotball. [[ArsonMurderAndJaywalking And they find his servant boy and ButtMonkey status for Team ITEM annoying rather than funny.]]

** Not to be left out, the third main character Shiage Hamazura. There are those who like him for being a true Level 0 unlike Touma [[BadassNormal who still kicks ass with nothing but wits, guns, and luck]] [[spoiler:(even defeating his own Level 5 Mugino in an epic fashion)]], which makes him something of an AudienceSurrogate like [[Manga/ACertainScientificRailgun Saten]], and they think his relationship with Rikou is very sweet while being amused by his ButtMonkey status in ITEM before (slowly) gaining more respect from them. There's also the fact [[spoiler:he's the first person to truly inconvenience Aleister]]. On the other hand, there are those who dislike him because he's not that attractive compared to Touma or [[spoiler:Accelerator]], he's a Level 0 with no cool powers unlike the rest of the male characters of the series yet manages to pull out wins against incredibly dangerous foes, finding his servant boy and ButtMonkey status for Team ITEM annoying rather than funny.

* FandomEnragingMisconception: Neither the name of Touma Kamijou's ability "Imagine Breaker" nor [[spoiler:the Invisible Thing/the Dragon]] is inspired by the American band ''Music/ImagineDragons''. ''LightNovel/ACertainMagicalIndex'' first volume came out in 2004, while Imagine Dragons band was formed in 2008.
* FandomSpecificPlot: Many ''LightNovel/ACertainMagicalIndex'' fans agree that [[EnsembleDarkhorse Frenda]] [[KickChick Seivelun]] from ITEM was underutilised, underdeveloped, and killed off in an undeserving manner. Some fans actually went out of their way to make FixFic where she survives for much longer and legitimately contributes to the plot, usually by forming a duo with the local TeamNormal Saten.

** LightNovel/KonoSuba, usually because of "I believe in Gender Equality" meme and [[https://youtube.com/watch?v=hLbVPpFYp3k the crossover game between the two series]].

* SignatureScene: A popularity poll ran for the best scenes in the franchise, with the results featured in the mobile game Imaginary Fest's second anniversary. The winning scene was Touma's PreAsskickingOneLiner "Grit your teeth, strongest" as he punches out the top esper Accelerator to put an end to his massacre of the Sisters.