After the game, Prier became a Demon Overlord to prevent another Maiden of Light/Dark Prince war.Yes, she helped Croix the Dark Prince fight his Enemy Within, but it's doubtful the Fallen Angel Calamity would give up that easily. Prier finds out that Calamity is after Croix, and so she takes steps to become the Maiden Of Light... and then opens a portal to Hell and kills enough demons that she becomes the Demon Overlord for her world. By substituting the Demon Overlord system for the Maiden/Dark Prince one, she challenges Calamity and takes over for evil. To maintain the dark energy needed to continue being a Demon Overlord without harassing her birth world, she challenges Alternate Netherworlds to fights, and main characters end up facing her in the Disgaea games. However, she has to cultivate a reputation of being a Blood Knight.
Prier is constantly purifying herself and Croix as the "Maiden of Darkness"; which requires constant fighting.Good Demon Overlord Prier came first. She purified the Dark Prince; and Croix kept his nature and sanity. However; the Dark Prince needs a Maiden to keep existing. So Prier used the "Overlord" system to commandeer the Maiden of Light position; as Maiden of Darkness. Keeping her sanity and purifying the Prince of Darkness was quite a feat; but her behavior and her world's "Chaotic Evil" Netherworld don't mesh. There's constantly a "drain" on her Demon Overlord status from using the purification feature; and if she ever stopped being Maiden/Overlord; Croix would succumb and pull Allouette (or a different Maiden of Light) back into the cycle. So Priere kept up her Overlord status by constantly repeating the action that originally transformed her; killing lots of demons. She's constantly on the lookout for good Demon Overlords to join their struggle; so she can keep her status and keep purifying Croix. Hence how even Good Demon Overlord Priere has a reputation of constantly looking for a fight.
Even without the bonus content, Prier is doomed to be a Demon Overlord... or worse.The N1 universe has a simple rule, you defeat it, you become it. This is why the Maiden has to die once she uses up all her powers. Since she exists only to defeat the Dark Prince, if she didn't die, she would accidentally inherit his title and eventually turn to darkness herself. This was done to prevent such a thing. However, Alouette and Prier found a loophole, and technically Prier is the one who defeated the Dark Prince, so she will eventually lose her soul to the darkness and become "Overlord Prier".
"Sea of Blood" Prier was faking it all along.Turning into a demon isn't enough to explain such a radical change of personality if you take Disgaea 2 and 3 transformations as examples. Prier had some minor changes after being crowned Overlord, but for the most part, she's faking the whole thing in order to sound tough. She was already doing the same thing with her own brother, going all Stepford Smiler when the subject of her dead parents came up. While it started with her brother, she pretty much doesn't want to look weak in front of others. She's doing the exact same thing in the Netherworld, especially since being the strongest is the only thing that's important. So she's just going around, trying to act like the demons in her Netherworld as a facade. The only problem is that it's pretty much obvious that the demons in La Pucelle's Netherworld act very different from the demons in Disgaea. The fact that Prier goes back to her normal personality in Raspberyl's Mode in Disgaea 3 seems to hint that she's still herself.
Noir is... AsagiForget being punished for his sins by turning into a Prinny, that's not enough. Instead, his human soul got reincarnated into Asagi and forced to endure game after game of slowly going insane due to crazy demon antics and getting screwed over and over. That's the ultimate punishment for trying to destroy the Gods, never being a main character in a series where being the main means everything!
Two things: A human lifespan is nothing compared to a demon's, and as Makai Kingdom showed us......humans can be reincarnated as demons after they die. So when a bunch of demons called Priere their Overlord, she got annoyed, forgot about it, and went on with her normal human life until she passed away. Upon where she was reincarnated as a demon like Seedle and Salome, and the demons that pronounced her the Overlord were waiting for her. So in the end she accepted because it's not like she had anything better to do. Eventually she went back to her own world, centuries later where her civilization had collapsed, and took it over as a benevolent ruler dedicated to creating human/demon harmony, so that another person like Noir won't have to show up and simultaneously ensuring a balance of light and dark. Portreene being an "incarnation of light" pretty much just exists at this point, and Calamity ether vanished or was beaten the holy heck out of. Her OOC-ness in the Disgaea games were the result of a bet: "Fine, am I acting like a demon enough now?" As for Eclair's downloadable in PSP Disgaea 2 and the Disgaea levels in PSP La Pucelle, respectively...Baal is probably mucking about with the timestream now.
There is both "Crazy Sea of Blood" Demon Overlord Prier, and "Maiden of Darkness" Demon Overlord Prier.Disgaea Infinite has Multiple Endings leading to events of various games; heavily implying that each event is an Alternate Universe shard. The same goes for Demon Overlord Prier. There's one where she went insane from the power of Darkness, and one where she did not.
Hero of Darkness Croix inspired the legend of the Dark Hero in Disgaea 2The Demon culture got a lot of the story wrong, and made up their own parts.
Poitreene and Calamity are the same entity and the world of La Pucelle isn't a human worldLight and darkness are just two sides of the same coin. Poitreene is the personification of pure light and Calamity is simply her Superpowered Evil Side that started to form in her heart after seeing all the evil humans could do. The world La Pucelle takes place in isn't an actual world, it's Poitreene's heart. The battle between the Maiden of Light and the Dark Prince is simply the two personas fighting to see who gets control of the heart, the other humans being "heart residents".
There is still a sliver of hope for Fallen Priere and Croix.This relates to Disgaea 3, where Priere and Marona meet by post-game content. Please recall that Marona can recall the dead, even if their soul has been destroyed. Whilst her heart has been lost and she wouldn't do it at first....afterwards, there's a chance. Would require Priere to open up about it though, and that's unlikely at best. There's also the risk that his soul would be all mixed up with Noir, given they both were obliterated in the same area. Would make for a heck of a boss fight. Anyway, the fact that they have actually met makes this possible, though not quite probable.
The Dark Prince is Fear the Great.The similarities are quite obvious. While Flonne said that Fear the Great had never been stopped before, she did say she read it in a report, so the failures could have erased. Which leads to...
The Maiden of Light is a virus possibly created by CalamityFear the Great is supposed to be unstoppable yet the Maiden of Light exists to counter it. Assuming Calamity, unlike Poitreene, is a physical being, she went against God's plan and decided to give the world another chance and created the Maiden, someone capable of taking on Fear the Great/the Dark Prince. Because of it, it failed and laid dormant until the next person had enough malice/darkness in him to re-activate. However God wasn't happy about it and declared Calamity His enemy, turning her into a Fallen being. This means Poitreene and Calamity have their roles inverted and she got the bad rep as to make sure people wouldn't follow in her footsteps. And even if Calamity wasn't involved with the Maiden, she could still have been created simply to mess with God's plan, thus screwing up the system.