Anti-Magic: A few variations: Kaiman, being hexed by Risu's Curse and Ebisu's smoke is immune to smoke. Chota's smoke reverses the effects of magic. And Noi can restore a body to its normal state (healing Shin's arm after a Magic User starts to melt it). And, if the Cross-Eyes are well informed, Noi's smoke could have undone Kai's transformation into a pie.
Ax Crazy: Shin during work, even if he actually uses an hammer.
Badass in a Nice Suit: En's family, being vaguely mafia/yakuza-like, embraces this, although there does seem to be a degree of leniency, as Shin and Noi seem to wear T-shirts or hoodies under their jackets quite a bit.
This only applies to the higher-ups. Fujita (when not at social occasions), wears shorts. And most family members wear some sort of garment that vaguely resembles a radiation suit.
Badass Abnormal: Kai typically uses his knives in combat, which is bad enough. But, when using stolen power to devastating effect or regrowing his own head, he becomes this.
Badass Normal: The Cross-Eyes. In theory, at least. Only Dokuga is consistently able to stand up to the stronger Magic-Users.
Barbie Doll Anatomy: Subverted; the series uses an extremely gritty, but comparatively realistic style.
Be Careful What You Wish For: Happens with Ebisu's parents. After Ebisu leaves home, they ask a shady magic user to create an exact replica of Ebisu to replace her. At first looking like a perfect copy, the fake Ebisu is actually a dangerous demon who goes berserk for very petty things, making Ebisu's parents flee their own home terrified.
Deconstructed with the wish-granting devil. He prefers granting stupid or selfish requests, so if you want your wish fulfilled you have to make it sound silly or greedy. When trying to get their friends healed, the Cross-Eyes wish for things like money. Natsuki, being Natsuki, decides to wish for Dokuga to be happy... and the Devil makes him laugh, sending his poison spit everywhere.
Subverted with Kai. Given that the Cross-Eyes idolize him and he gave them a reason to live, one would expect him to be A Father to His Men. If he finds out that one of his comrades have magic he wants, he will kill them just like anybody else.
Beware the Superman: Magic users experiment on humans, with humans for the most part unable to do anything about it. High class magic users like En also appear like this to weaker Magic Users, like the Cross Eyes.
Thirteen freaks out when Nikaido returns to the Hole with a bunch of (friendly) sorcerers.
The devils are this to everyone, even the strongest magic users are afraid of them and are forced to worship them. Kneeling down before a devil slightly reduces the chance of being killed or horribly mutilated for fun.
Store, in turn, is this to devils. It seems pretty tame and often does business with them, but they can't quite get over the fact that It can kill them.
Big Eater: Kaiman, Shin, Noi, even the little Ebisu can eat quite a bit.
Asu eventually cheeses off Chidaruma too much and loses his devilhood. Of course, you have to be an elite magic user to become a devil in the first place.
Bullying a Dragon: When a pair of bullies pick on Fujita and Ebisu, knowing full well that they work for En. Now, this would be fine, seeing as Fujita is a weakling... but his friends, Shin and Noi are not.
Butt Monkey: Fujita. Upon hearing that he will be sent on a dangerous mission, the other members of En's Family, somewhat surprised that they were not chosen, conclude that he was chosen because he is expendable.
Darker and Edgier - Once the Cross-Eyes take over the Magic Users' World and start killing off Magic Users. Arguably, the trend began about when En curb-stomped Kaiman, leading to the return of Kai.
A Day in the Limelight - The Bonus Curse chapters occasionally focuses in secondary characters like Natsuki, Risu and Ebisu.
Death Is Cheap - En has a petfamily member that can bring Magic users back to life, so long as their Devil Shaped Tumour remains intact. Though this has had surprisingly little use.
Disc One Final Boss - From the beginning it looks like that En is the "Big Bad" of the series (which isn't saying much thing considering the Black and Grey Morality in this manga), but after several volumes later it turns out that the actual Big Bad is Kai as he schemes to steal the abilities of every Magic User. But then by the end of Volume 15, it seems like that the real actual Big Bad is Chidaruma.
Dissonant Serenity - Nikaido, who looks positively bored while killing people in horrible ways.
Becomes positively horrifying when, as Kaiman accosts poor little Ebisu, Nikaido stands there with a massive smile on her face
Face of a Thug - Both played straight and averted. When masked all the cast look like it's out to get you (it probably is actually...), when unmasked they're all pretty cute. En even ventures into cute little boy territory in a flashback.
Facial Markings - The Cross-Eyes Gang have — you guessed it! — crosses tattooed over their eyes. This becomes important, as Kaiman has these tattoos, as well.
Fantastic Racism - Magic-Users and Devils consider humans to be little more than trash only fit for performing experiments on or eating.
Played for Laughs when Kawajiri (Asu) says something along the lines of "Shut up, human" to Thirteen.
For the Evulz - Devils mess with people for the heck of it, ranging from throwing crap at them to growing to enormous size and stepping on them. To be fair, this basically appears to be their job description.
For Science! - Kasukabe. He even tells Kai that he wants to help him in order to study him (and was responsible for turning Kai, then Ai, into a magic user.)
From Nobody to Nightmare - Ai. Started out as a kid in the Hole who wanted to be a Magic User. Ends up ruling the Magic Users' world.
Gag Boobs - Ebisu orders a pair of these along with an outfit in order to compete with Noi.
Kai. Whenever he appears, everything seems to twist around, Magic Users feel ill, and see the headless/neckless man that Kaiman/Aikawa meets in his dreams. When he changes from Aikawa to Kai, his head explodes off of his body.
Jekyll and Hyde - It is gradually revealed that Kaiman, Aikawa and Kai share the same body.
Jerk with a Heart of Gold - Applies to many characters, but Tanba is possibly the most notable example. Despite beating his employees for incompetence and constantly insulting them, he actually shows concern for them. He is also the one who helps Kaiman after he comes alone to the world of the Magic Users to find about his past.
Lethal Joke Item - Magic power actually; Fukuyama can beat opponents instantly by turning them into pies. He beats some of the Cross-Eyes this way, and even Aikawa (who admittedly let it happen). En's mushroom power is similar, just substitute mushrooms for pies. He can also propagate them through spores without directly using smoke. This bites Kaiman, who is only immune to smoke, in the butt.
Natsuki's magic is large and blobby, but becomes less funny when even Risu's Curse ability can't hurt it.
Masks are a status symbol in the magic-users' world. If you prove your magical skill to a demon, it will make a mask for you. Those with lesser powers emulate this with home-made masks, such as Ebisu and Fujita.
Mad Doctor - Kasukabe seems pretty happy about having made his magical door out of humanMagic-User skin.
Made of Plasticine - Sure, Noi is strong, but it's supposed to be nigh impossible to karate-chop a person in half.
Meaningful Name: The Cross-Eyes have a few. Dokuga, a Poisonous Person, is the name of a poison moth. Ton, a fatty, is the name of a pig. Lampshaded during their part-time jobs, where they each where costumes related to their names. Shin, whose name means heart, wears a heart-shape mask.
Mega Manning - Ai. In possibly the most horrifying manner imaginable.
Number of the Beast: Comes up so often that it's more of a red herring. Conversely, pretty much any three-digit number other than 666 is important.
One-Winged Angel - Kai. By fusing with something he made out of flesh and a bunch of heads.
Perpetual Poverty - The Cross-Eyes in Berith. They keep the light off as long as possible to save money and take whatever (crappy) jobs they can get. They almost lose their house until they (accidentally) kill the landlady. Justified in that they need to keep a low profile and cannot take any major jobs.
Person of Mass Destruction - En, whose mushroom power covers an entire village with mushrooms during his battle with Kai. The Cross-Eyes Boss also qualifies.
Phlebotinum Pills - The black powder, which dramatically enhances the strength of Magic Users.
Pint-Sized Powerhouse - Nikaido as a child. She was even able to take down adults in hand to hand combat.
Poisonous Person - Dokuga. He takes baths after his companions and eats alone to avoid poisoning them. He does manage to kill an entire party of Magic Users by taking a bite of something and throwing it into the punch bowl.
Reincarnation - Kai/Ai/Kaiman/Aikawa. Whenever he gets killed, a new head appears on his body. Though the same personalities reappear, his inner world is filled with various corpses, presumably previous personalities. Occasionally, one of these return, such as the original one, Ai, who is rotting.
Ret Gone - What happens to Nikaido's surrogate sister. She also erases her entire past. Nikaido manages to make it better though.
The Revolution Will Not Be Civilized - The Cross Eyes, who started out as the oppressed in Magic User society, stigmatized, tormented and forced to live overall sucky lives because they lacked magic power. Once they gain political power, Kai decides that it is time to begin the slaughter. Mountains of corpses result.
Surreal Horror - It gets particularly blatant in dream sequences, when it gets harder and harder to tell who is speaking to who, or when it was supposed to take place, or what the hell that actually is. The author's art style makes a good part of the main story have this feel to it as well.
Sympathetic Murderer - Shin, whose father was killed simply because Shin's mother was a magic-user. Shin took revenge by murdering the entirety of the anti-magic squadron, thus dooming the entirety of the Hole. But he's still rather sympathetic, probably because of his easygoing personality.
Training from Hell: The Devil Exam, which involves wearing massively heavy armor and carrying around giant bats.
It's also a literal example: devils live in an actual Hell.
True Companions - The En family, Kaiman and Nikaido, Dokuga and his friends.
Urban Fantasy - A variant in some way. The Magic Users ride on brooms (basically flying, smoke-powered broom-shaped motorcycles) and use cell phones. Plus, the whole setting reminds a cyberpunk-like esque universe.
Villain Episode - This manga concentrates just as much on the "villains" as the "heroes".
Villains Out Shopping - The En family will often be shown engaging in everyday activities. In the case of Shin and Noi, they will be at some fancy restaurant. En runs his many non-evil businesses, and Ebisu plays with Kikurage. They also actually go shopping.
The Cross-Eyes in Berith (Dokuga, Ton, Tetsujou, etc.) live in poverty and try to find whatever jobs they can. For much of the series, their appearances involve keeping the lights out as long as possible, freaking out because they missed recycling, or finding various strange jobs (termite extermination and hot springs workers).
Weaksauce Weakness - Rain physically weakens Magic users. When Kai going One-Winged Angel makes it rain in the Magic Users' world, most of the Magic Users start collapsing and feeling ill. Kai seems to have absorbed some of the rain's toxin, as being near him gives Magic Users the same effect.
Witch Species: The series has a very biological approach to magic: Magic Users have a special organ in their abdomen for producing magic smoke, with smoke ducts running along their arms to their fingertips. They also have a tiny devil-shaped tumor in their frontal lobe.
"With Our Swords" Scene - Fujita gets loaded up with Family magic before he goes to recon the Crosseyes leader. Subverted, in that he has to leave it all behind, so that he doesn't fight recklessly.
Wretched Hive - The Hole. The gritty artwork makes the entire place look dark and dirty. Houses are cobbled together out of who-knows-what or are part of a disheveled urban sprawl. Though good people can be found, having to dodge the crime and the zombies as well as Magic User attacks makes it not so fun to live there.