These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Arc Fatigue: Due to being a monthly manga, many have felt that the chapters do not provide enough content to satisfy a monthly release and that each chapter is paced like it would be more suited for a weekly manga. Readers would often get bored, and lose interest during certain parts of the manga. It could be during the Impure King arc where people found the build-up and the climatic battles to drag on much longer then they should have, it could be the school festival chapters following the previous said arc for being Padding chapters until the next Story Arc starts up, and even during the current Izumo arc which many have felt has been stuck-in-place the past several months building up to the final confrontation.
The anime's opening "CORE PRIDE" by old favorite J-Rock band UVERworld.
The second opening, "IN MY WORLD" by ROOKiEZ is PUNK'D is just as awesome as the first opening.
Not only the openings are awesome, the soundtrack itself deserves a mention, too. See for yourself.
UVERworld makes a triumphant return to the series with the theme song to The Movie, "REVERSI".
Cliché Storm: Be ready for for A LOT of recycled Shōnen tropes. Not that this is a bad thing. To the series' credit, many of the tropes are occasionally twisted in new ways to keep things fresh. It arguably succeeds in this end as well.
Especially done well with the characters. All of the main casts fit pretty well into established character tropes, but are fully fleshed out as opposed to flat stereotypes.
Complete Monster: Dr. Michael (Mihaeru) Gedouin, the resident Mad Scientist of the Illuminati, spends the entirety of the Izumo Rescue Arc proving himself to be the most selfishand utterly depraved human being in the story. In flashbacks, he and his team abduct Izumo, her sister Tsukumo, and her mother to use as subjects in his research on the elixir of immortality. He subjects their mother to horrific experiments that reduced her to a broken, bloody shell of a person, while threatening to use Tsukumo (who was two years old at the time) next if Izumo did not follow his demands. When the heroes storm his laboratory, they discover that he has been brainwashing people who visit the town near the lab and using them as disposable fodder for his experiments, turning them into shambling, semi-consciouszombies. When called out on his atrocities, he actually employs a Humans Are the Real Monsters argument to defend himself, considering himself to be above the people he uses as guinea pigs. Further, it is repeatedly show that his only motivation for his evil is to earn approval from Lucifer. An immature, self-centered bastard who relishes the suffering of others, Gedouin stands head and shoulders above all previous villains in terms of monstrosity, and his actions even disgust Lucifer.
Cuteness Proximity: Meta-Example; if OkumuraRin comes up in a conversation between fangirls, expect the word "cute" to show up 9 times out of 10.
Meisa's Kuroki's "WiredLife" is another contender.
Ensemble Darkhorse: Renzou if the merchandise has anything to say about it. This guy is snuck into pictures alongside more central characters of the show when his fellow companions who've arguably been given more focus, Bon and Konekomaru, are nowhere in sight! There's even an official letter set where he appears more often than the main character, for some reason. In the official poll he ended up being the fourth most popular character in the series after Rin, Amaimon, and Yukio.
Fans seem to have taken quite a large interest in Amaimon, to the point he managed to place second in the popularity poll, while Yukio got first place and Rin ended up in third.
Juuzou and Kinzou, Renzou's older brothers, are very popular for being introduced not too long ago and with only moderate, and moderately important, screen time. In general, the Shima brothers seem to be very popular amongst fans.
Expy: Rin does have a resemblance to a certain Public Domain Character. Flaming Sword? Check. Blue fire? Checknote Obscure, but true, as the old verbal charm used to invoke him refers to his "flaming sword of cobalt blue.". Incredibly protective? Check. Willing to help all in need? Check. A tendency for arrogance? Check. Popular? Fandom says yes. Who does he greatly resemble? No one else but Archangel Michael himself! And the recent Story Arc introduces the Demon King of Light...aka Lucifer as the current Big Bad.
All those times where Renzo was picked on and treated as pure Comic Relief? Those moments where he was shown to be a "comedic" The Unfavourite? Yeah, about that not so funny now it's turned out he's been seriously damaged to the point of turning to an evil organization and being a Stepford Smiler. Not to mention if you look at from a "real world" perspective, his treatment reeks of family abuseandneglect, as well he shows signs of being possibly depressed.
Hate at First Sight: A meta-version; within a few panels of Angel's introduction, the fandom already have him on their list of most hated characters in Blue Exorcist. And he's above Satan. Yes, he's that much of a jerk. Seems to be slowly transitioning over to Love to Hate, mostly because he's an idiot (worse than Rin as a matter of fact) and he ended up placing fifth in the official popularity poll.
For Gedouin every one just flat out hates him; and is grossed out by him.
One of the first filler episodes in the anime involves a Kraken attacking a coastal town. Guess what the first chapter after the whole Impure King arc involves?
It's funny think that Hiroshi Kamiya (Mephisto) spouts any German used in the show when Amaimon's voice actor, Tetsuya Kakihara, was born and raised in Germany and is as fluent in German as he is in Japanese.
The Gecko Ending of the anime had Satan attempting to join Gehenna and Assiah together through a large Gehenna Gate to create a "new world". Guess just what's been revealed to be the Chief of the Illuminati's plan?
Ho Yay: Bon/Rin, what with Rin going on about how "cool" Bon is, getting all wide eyed and blushy when he does something awesome or nice and then him getting the most depressed over Bon being angry with him over his Son of Satan status. And Bon doesn't skimp on it either; he blushes the first time he's nice to Rin, as a lot of Held Gaze moments with Rin, his treatment of Rin can be seen as rather Tsundere and his declaration of friendship comes across almost like a love confession. Which conveniently helps Rin get past a mental block...
Shiemi's strong desire to befriend Izumo, and willingness to be used as a doormat to that end. Izumo's tsundere and Defrosting Ice Queen towards...well, everyone, but especially Shiemi.
Izumo and Paku, on the other hand, seem to be nearly canon. Izumo initially had no interest at all in associating with anyone but her best friend Paku.
What the Hell, Townspeople?: In order to save his friends from Amaimon, Rin reveals his secret nature. Despite proclaiming their friendship only 3 chapters (a couple hours In-Universe) before, his classmates start ignoring him in a silent Take That. In the anime this is short but in the manga Rin is ignored for several chapters (daysIn-Universe). Only Izumo still talks with him during this time and mocks the others for their hypocritical statements.
Although to be fair, he was revealed to be the son of Satan, the mortal enemy of all exorcists, and some of them had their own reasons for ignoring him.
On the other hand, it is still really harsh to do that to a friend that you've known for awhile.
Subverted in the anime with Ernst. According to him, he lost his face, his daughter, and his freedom all at once. It took YEARS for him to climb all the way back up, and the only thing that gave him the courage to do so was his photo of his grandchildren (whom he'd never met.) However, everything he said that he went through, aside from having his face burnt off, were all Blatant Lies.
And, now, with the latest arc Izumo definitely counts.