Disgaea: Afternoon Of Darkness Codes -

Etna mode
Highlight the "New Game" option at the title screen, then press , , , , , , . Etna's voice will confirm correct code entry. 
Alternately, complete the game after reading Etna's diary in each chapter. 

Unlockables
Bonus classes
Complete the indicated task to unlock the corresponding class.
Angel: Get Female Cleric, Knight and Archer all at level 100 or higher.
Archer: Get level 3 or higher in Bow Weapon Mastery.
EDF Soilder: Get level 30 or higher Gun Weapon Mastery.
Galaxy Mage: Get a Prism Mage to level 50.
Galaxy Skull: Get a Prism Skull to level 50.
Knight: Get Female Warrior and Female Mage both at level 10 or higher.
Majin: Get a Male Warrior, Brawler, Ninja, Rogue and Scout all at level 200 or higher.
Ninja: Get a Male Fighter and Male Warrior both at level of 10 or higher.
Prism Mage: Get a Star Mage to level 35.
Prism Skull: Get a Star Skull to level 35.
Ronin: Get a Female Warrior and Female Fighter both to level of 20 or higher.
Scout: Get two Fighters or Warriors, Males or Females each to level 5 or higher.
Star Mage: Get a Fire, Ice and Wind Mage all to level 5.
Star Skull: Get a Fire, Ice and Wind Skull all to level 5. 

Alternate endings:
Complete the indicated task to unlock the corresponding ending sequence.
Good Ending: Complete the game without killing any allies.
Dark Assembly: Persuade by Force 100 times in the Dark Assembly.
Etna Heroine: Kill 100 or more allies before Episode 5's Ice Queen Battle then choose to kill Maderas.
Flonne Tradegy: Kill 50 or more allies before Episode 3 and the Lavish Hall battle. Choose to Kill Hoggmeiser.
Overthrow Earth: Clear human world.
Bad Ending: Defeat the Item God on the 100th floor of a legendary item.
Midboss Ending: Lose to Midboss in your first encounter.