The Netherworld... A lawless world filled with vicious monsters. The number of Netherworlds has expanded with the rise of demons powerful enough to rule such worlds... the Overlords. Now, another world is about to fall prey to such darkness. —Opening Monologue
While Etna Mode was an Alternate Universe, Axel's Dark Hero Days actually tell of what he did just before the plot. (In the post-game, the people who joined him can join Adell)
Back from the Dead: Zenon found a way to resurrect himself by converting a population's humanity into his life force. Those affected became demonic, but he refused to call them demons. "Altered Humans."
Batman Gambit: Fake Zenon chose to sponsor a fake competition to erase all competitors for the throne. Rozalin attending the competition in Adell's escort caused it all to backfire to the point where he actually LOST to the intended target, Etna.
Real Zenon was once one, until she tired of the endless bloodshed.
Bonus Level Of Hell: The Land of Carnage, which gives the enemies a 2100+% boost in power. All of the enemy characters have a level boost of 2100% base plus two hundred, plus all their stats are doubled on top of that. Have fun.
Bonus Boss: Laharl, Etna, Flonne, and a bunch of other Nippon Ichi characters. The PSP remake adds more, for a total of twenty-six.
Brick Joke: In Axel Mode, one of his baby brothers, Axeleration, is a Genre Savvy little know-it-all who loves sharing his insights on the entertainment business. Axel is horrified that he doesn't "act like a proper child". In the last act, his other baby brother Axident, who's been cooing and crying all this time, abruptly complains that it's hard to act like a baby, and Axel praises him for staying in character for so long.
Brilliant, but Lazy: Adell is entirely capable of being intelligent, as he demonstrates with the Inevitable Tournament's ungodly complicated geopuzzle and his status as the group's Only Sane Man, but usually turns his brain off because solving everything by punching the crap out of it is generally easier — and more fun.
The Computer Is a Cheating Bastard: When you magichange in the remake, you only have 2 turns to wield the monster-weapon (3 if you pass the once-per-resurrection bill for the monster). If the computer magichanges enemy monsters, they keep them forever.
Cursed with Awesome: Zenon's curse. While the negative effects (global amnesia, lack of conscience, Zenon can cast Life Drain on you) are pretty bad, Hanako points out that the deal of getting to be a demon is pretty sweet for anyone born and raised under it. How sweet? Enough that she's a-ok with forgoing the chance to become human again for the opportunity to become the next Etna.
Dark World:...the...um....Dark World; as well as the Land of Carnage.
Defeat Equals Friendship: In several ways. Most of the story characters have to beaten, or at least, foiled first. Downloadble characters (save one) have to be roughed up, and other extra characters that you can get in the Updated Rerelease are initially Bonus Bosses. Further, you can capture monsters by tossing them into the Base Panel and whupping the tar out of them.
The game takes time to point out that Adell really isn't an Idiot Hero when he easily unravels the geo puzzle in the colosseum. The explanation given is that just because he prefers to rush in with his fists doesn't mean he's incapable of thinking it out when he needs to.
Dirty Coward/Fake Ultimate Hero: Axel runs away numerous times whenever he's getting his butt kicked. He also claims to be a famous "Dark Hero", but nobody really thinks of him as famous, except for the Director who's always following him around and probably has a homosexual crush on him.
It eventually gets revealed that the whole point of a Dark Hero is to be underhanded, sneaky, and repulsive: in other words, all the qualities that evil just loves. Though, judging from some of the other games, not toorepulsive.
Disc One Nuke: Pleinair. Being Level 100 and using her at Early game will solve till everyone catches up.
Disproportionate Retribution: The cause of the entire plot. Fake Zenon loses a fight to Real Zenon. As revenge, Fake Zenon initiates an incredibly complicated plan that involves tracking down and kidnapping the innocent reincarnation of Real Zenon, then raising her as an air-headed, pompous fool. It's so crazy that it actually works, at least until Adell starts pulling the thread.
Also, if you win the first fight against Laharl, he destroys the entire world.
Fallen Princess: Rozalin. She goes from living in a huge mansion being attended to by hundreds of servants to essentially being stuck in the Netherworld version of a small Kansas town running around in the muck.
Fanservice: The Nekomatas and Succubus are back and the Magic Knight got a breast size boost. Then we have the new human classes Kunoichi and Beast Tamer. If you want to go there, Flora Beasts as well.
Fantastic Racism: Most "true" demons refer to Veldime inhabitants as "Altered Humans."
Fetish: When summoning Saphire as DLC in the PSP release, it's noted that since Adell summoned two princesses, he must have a thing for them.
The Dog Bites Back: For treating them like crap, killing them whenever she's bored or angry, and for being a bitch in general, the prinnies waste no time in betraying Etna once a botched summoning turned her into level 1. Everyone else is surprised at how hard the prinnies are working just so they don't have to work for Etna again.
Foreshadowing: When you first meet the Prism Rangers, Prism Red says that his demon detector says that Adell is a demon. Everyone says that it must be broken. It isn't.
A subtler one is the fact that Adell's ears are covered by his hair, making it impossible for the player to tell if he's human or demon. It did make it easy for the player to initially believe that Adell was the only human left on Veldime.
Although, Word Of God states that he has rounded ears due to a genetic deformity.
There's another one halfway through the game where Rozalin says "...do you suppose he (The real Zenon) may have been tricked by the faker and is imprisoned somewhere...?"
At one point, Hanako asks Rozalin if she could one day become as strong as Etna. Rozalin tells her she could become even stronger. Cue Dark Hero Days, which features Demon Lord Hanako, widely considered to be the best unit in the game.
Of course, as mentioned under Exact Words: Mom cast a spell to summon Overlord Zenon. They got Rozalin.
Forgot I Could Fly: Subverted. Rozalin can fly, but not for long enough to help when she falls off a cliff.
Also, your crimes and penalties actually ties into the ending you get into the game. It makes sense, given that the worse ending implies that the player played Adell as committing crimes and killing allies left and right. Whereas the Good End actually reflects on how the player cared about your allies.
Rozalin and Adell start out hating each other, and this is reflected by the fact that as the game begins they only have a 1% chance of engaging in a Team Attack together. As the story progresses and they grow closer, this slowly climbs to 99%. If you get DLC Almaz and Sapphire for Dark Hero Days, they too have a 99% chance of team attacking, due to them being married by the end of Disgaea 3.
Get a Hold of Yourself, Man!: Adell does this to Rozalin after she totally wigs out in a battle against Laharl and starts to attack her teammates. This is better when you realize that she reverted back to Overlord Zenon, meaning that Adell just Bright Slapped the God of all Overlords. And it worked.
"Beauty Qu- er...Demon Lord Etna?! From Zenon, of all people.
Gratuitous English: In the Prism Rangers bonus battle, Prism Orange parodies this concept by speaking entirely in Engrish. In the original Japanese version, he spoke like a stereotypical foreign Japanophile.
Honor Before Reason: Adell will protect anyone and everyone he makes a promise to, no matter what it takes. His shameless sense of honor also works as an in-game combat bonus: his attacks get stronger against enemies at a higher level than him.
Yukimaru frequently attempts seppuku whenever she thinks she failed her mission. She gets over it.
Hostile Show Takeover: After playing through the game a bit, various secondary characters will send proposals to the Dark Assembly to become the Main Character. If the proposal is passed — and there's usually a very good chance of it happening — a Non-Standard Game Over is triggered (You get a cool item if you defeat it).
Hot Blooded: Quite a few characters, but Adell especially. He can even set enemies on fire through sheer hot-bloodedness.
The Immune: Adell is the only human in the world who isn't affected by Zenon's curse because his parents are demons, and so is he; you obviously can't turn somebody into a demon when they already are one.
Insult Backfire: Any derogatory statement about Mom's lack of conscience will invariably be met with, "Damn straight, I don't — Zenon took it. Now either go kick his ass or shut your trap."
Interface Screw: The map during battle against fake!Zenon is oriented at a forty-five degree angle, compared to the rest of the game's maps (likely for the visual aesthetic), and your directional controls are altered to match.
Internet Backlash: The NA DLC release. Not only did it suffer from bugs, but NISA also decided to cut out Gig, Dark Eclair, and Miabelle due to technical issues. This did not sit well with most fans.
Same for Axel and his little bro. He will willingly give up fame and fortune to tear your ass apart if you threaten him.
Large Ham: Overlord Zenon in the dub. Both real and fake.
In the Japanese version as well, being voiced by Norio Wakamoto and all... The fake one, anyway.
Loads and Loads of Characters: The PSP version of Disgaea 2 is looking to beat Disgaea 3 in this aspect. Alongside the returning playable characters, the optional bosses that were originally not playable in the original in the PS2 version are now playable, many of whom became DLC in Disgaea 3. Additional bosses have been added including Mao, Raspberyl, and Mr. Champloo from Disgaea 3 as well as the Disgaea 3 version of Asagi, all of them playable. And if that wasn't enough, Disgaea 2 is also getting Downloadable Content.
Lost in Translation: The bill to fight Zetta is "Meet The Strongest Overlord." Zetta's self-declared title in Japanese pretty much means that, so it ended up summoning him.
No Fourth Wall: Rozalin asks Adell where his confidence comes from; is he descended from heroes? is he level 100,000,000?
Noble Demon: Axel might arguably be considered one, as a major motivation behind his actions is his sick mother and siblings.
Rozalin is just a snob at times; she honestly cares about Adell's family. As for Adell, well, as Etna puts it; they have one of those kinds of relationships.
For all her display, Etna does let Adell go when she beats him and it's a Non Standard Game Over if he beats her only because it drives the plot Off the Rails. If you're paying attention, you'll also notice that she takes the hit from Zenon's super blast in the ending in order to protect Hanako.
Referenced a couple of times in the manga adaptation. In the second volume, upon hearing that Hanako is unable to cook any meat due to her family's income, Rozalin forces Tink to lend her money. In the fourth volume, Rozalin confesses to fake Zenon that the birthday cake he sent her for her birthday when she was six was too sweet and hasn't been fond of sweets ever since, which may have led to her preferring meat instead.
Redemption Demotion: When Etna first shows up, she is an extremely powerful boss-type character that's impossible to defeat on most first playthroughs. She reappears later on in the game, but is reduced to level 1 and given crappy equipment, and she forces herself into Adell's party to gain her levels back. Their initial exchange upon her return is rife with Lampshade Hanging. This can also be subverted using the New Game Plus feature which allows for your previous party members to rejoin at the level they were during your last playthrough, how does this affect your series well, if your Etna was at level 9999 and had all the best weapons and armor then she'll rejoin your group in that chapter at this level.
Save the Princess: Subverted. Axel makes the assumption that Princess = Must Be Saved, even if said princess is with her "captor" willingly (Rozalin). The situation ended in comical pain.
Seppuku: Yukimaru is a little too eager to commit suicide after 1) your group defeats her and 2) the odds against surviving an encounter with the fake Overlord Zenon don't look good. Adell has to talk her out of it both times.
Serial Escalation: The original Disgaea 2 has a way of constantly making each challenge worse than the last. Starting from the first fight with Axel culminating in the Bonus Boss Baal, but every time each battle not only gets consistently harder, geo effects are played with, enemy equipment is pushed to its limits, and eventually stats are just ridiculously allocated on the enemies. It finally gets Up to Eleven when Pringer X is introduced on the port "Disgaea 2 Dark Hero Days" as a boss who is just overall ridiculously difficult, but even after winning the player is forced to refight 8 of him with maxed out stats in every category or the battle doesn't count in the dark record.
Stay with the Aliens: It's stated in the Good End that Hanako remained a demon so she could apprentice under Etna.
Sound Only Death: The Worst Ending has a post credits sound only epilogue where you can hear Hanako trying to reason with the now possessed Adell. It gets worse from there when in the Japanese audio you can hear Adell kill both Hanako and Taro, then eat them complete with the gory sound of there flesh being torn apart.
The Big Damn Kiss: After 13 chapters of UST, Adell embraces Rozalin in the good ending to calm her "True Overlord Zenon" form. She turns back to normal from Adell's Cooldown Hug, and the following dialogue occurs:
Rozalin: *sob* Sh- Shut up... you're an enemy! I can't trust anyone...
What Could Have Been: Disgaea 2 was originally going to star Laharl, Etna, and Flonne again, but according to Word Of God, they had felt that they had done everything that wanted to do with them and decided to create a whole new world with new characters and everything in order to bring in new people to the series.
Worth It: Axel says this in not so many words after attracting the vengeance of almost every overlord ever for the "Fake Zenon" stunt he pulled in the last chapter. One of the last images the game gives us is Axel riding off with dozens of fangirls and an expression that just screams, "So fricking worth it!"
Wrong Genre Savvy: Adell assumes that he'll be able to beat Zenon despite his low level because he's the only human in Veldime who hasn't been affected by Zenon's curse, and thus he must be the main hero character who triumphs against all odds. He's wrong in regards to why he's immune to the curse, but the confidence he gains from his Determinator attitude certainly contributes a lot to his eventual victory.