Tsunenaga Tamaki, formerly a reclusive and indifferent otaku, becomes a tyrant who cares for absolutely nothing but himself and his games. When the Great Tokyo Earthquake occurs, he leaves his mother to die so he could find a backup generator. He is also responsible for designing the prison and forcing prisoners to participate in Death Games by poisoning them upon arrival and only awarding antidotes to their winners. As a sadist who sees defeating the Wretched Egg as a game, he also creates the Forgeries, prisoners who are turned into artificial Deadmen and brainwashed into obeying Tamaki's orders.
Rinichiro Hagire, the prison's real director, is a sadistic, sociopathic Mad Scientist who will do anything for his research. Using Shiro as a guinea pig for research on how to improve a person's immune system, Hagire becomes obsessed over his subject's ability to regenerate. From crucifixion to vivisection, Hagire grows fond of conducting brutal experiments on her and becomes directly responsible for her becoming the Wretched Egg. He also manipulates Chan and En to use their Branch of Sin to invade and override other people's bodies and personalities when he's on the verge of death, and cannibalizes the remains of defeated Deadmen.
Germans Love David Hasselhoff: While the manga remains popular in Japan, the anime was not received well by Japanese audiences during its original run. Meanwhile, the anime had become a Sleeper Hit in the United States and rivaled Bleach as the biggest draw for the recently revived Toonami, while the English manga release withered to do poor sales and was discontinued after only 4 volumes. Although given the anime's high ratings in the States, it's little wonder why Viz Media has decided to crank a Network to the Rescuefor the manga. It should be pointed out that Bleach was currently airing the Zanpakutou/Sword Beast arc in the U.S. along with Deadman Wonderland, but Americans loved the sadistic prison anime nonetheless.
Harsher in Hindsight: Any of the interaction between Ganta and Shiro after knowing that Shiro is also known as "The Red Man." The revelations regarding the real personality of Shiro in Chapter 55 only makes it worse.
Jerkass Woobie: Minatsuki in spades, once herbackstory is revealed. Shiro also counts, if you consider her and her Wretched Egg personality to be one and the same.
SHINY SHINY note Taken from the upbeat ending theme. Placing the words over a particularly violent/gruesome moment from the episode or playing it over said moments.
G-Cup titties. note In Episode 1, when an inmate asked what Makina's breast size was, she simply said "I'm a G".
"DON'T MESS WITH THE HUMAN CALCULATOR!" note In Episode 10, during Rokuro's massive freak out, he tells Senji this when said person's branch of sin doesn't work.
Rokuro in general is starting to become this. note Rokuro's over the top mannerisms and narmy animations which are very similar to Higurashi in style coupled with how many funny lines he has in the English dub have led to this.
"DEATH IS ROCK AND ROLL!" note During Episode 12, Genkaku's line in the English dub is switched from "DEATH IS SALVATION!" to said line. It's pretty obvious why.
"Heyooh fahking guyz!" note Genkaku's Engrish in Episode 9 right before shoots and kills some of people from Scar Chain.
"I WANNA LIVE!" note Ganta screams this in the first episode. Usually this is said when someone's playing a video game and they keep on dying.
Moral Event Horizon: For Shiro, murdering Ganta's classmates out of pure jealousy. It is for this reason that she feels that Ganta must absolutely kill her.
Watch Episode 6 in the English Dub and just try to take the rant Minatsuki has about her mother abandoning her for the flowers seriously.
Ganta walking out of from his court sentence would've been sad, if not for the fact that someone just decides to up and egg him while he's being escorted away.
Rokuro's Villainous Breakdown / Freak Out! in Episode 10. It was supposed to be unsettling, we think, but since his craziness went that far, came literally out of no where, with almost no hint that he actually like this, and the fact that both voice actors, Jun Fukuyama and David Trosko, are clearlyhaving too much fun during it, cemented the scene's status into this trope forever.
Also, the name of the event, "Carnival Corpse" is both awesome and cringe inducing.
Never Live It Down: There are people that are still mad at Ganta for punching Shiro because she destroyed the data chip.note It was actually a bomb built by Rokuro, so she had a good reason to. These people have usually only seen the anime, though.
No Yay: A subset of the fanbase ships Genkaku with Nagi. Genkaku killed Nagi's pregnant wife in cold blood, as well as torturing him and making him remember that his unborn child was dead. He then stabbed his friend, and then killed him. Most fans love the pairing regardless.
Paranoia Fuel: A mad bomber/slasher/whatever busts into your third-story classroom through the window and kills everyone in your class except you. You wake up injured to the bloody mess left behind as the murderer gloats by showing you your girlfriend's severed head. You pass out and wake up in the hospital where you are then arrested for the murders. You protest your innocence, but everyone who could corroborate your story is dead, and no one, not even people who have known you your whole life, believes you- you aren't even sure whether or not you believe yourself. You're sentenced to death for a crime you didn't commit, and your friends' parents have to be restrained to keep them from beating you to death on the spot, only for your cell phone to drop out of your pocket and reveal a video you know nothing about incriminating you by showing you bragging about the murders to your lawyer. The frame-up is so convincing you start to believe you're insane.
Squick: Are you kidding? Deadman Wonderland is Squick: The Manga.
Chapter 43 of the manga treats us to the sight of Wretched Egg laying on a bed, naked, casually going over a summation of her recent fight with Ganta. Cue Hagire touching her naked body. And to make matters worse? Wretched Egg doesn't seem bothered by it. At all. In fact, she almost seems okay with it. To recap, this is a guy that has put her through hell, to the point where he's responsible for that side of Shiro even existing, and she's apparently so used to him molesting her that she doesn't even think to resist or even object.
Superlative Dubbing: The dub was so good that it managed to cause the anime to become a breakout hit in America with many people wanting to see it get a second season. It added a lot more humor, and witty dialogue, and the voice acting is very good, and some would argue even superior to the original.
Rokuro. The fact that he was a One-Scene Wonder and a classic case of What Happened to the Mouse? only makes it worse, when a lot of fans would have at least liked to see what became of him. Or even how he became so crazy to begin with.
They Wasted a Perfectly Good Plot: After Genkaku was revealed to have survived Ganta's Ganbare Gun, he is never mentioned again. Quite a few fans didn't appreciate being teased that an Ensemble Dark Horse could have made a comeback in the future but were left hanging, and will now probably never know his ultimate fate.
What an Idiot!: Yeah Rokuro, just announce that the data chip was a bomb to Scar Chain when they had absolutely no clue that it was. What could possibly go wrong?
What Measure Is a Non-Badass?: A lot of people keep forgetting that Ganta's fourteen and was an everyday middle school kid before being put in DW. Instead, they call him pathetic, and wimpy, and that 'he needs to grow up'.