Disgaea 3: Absence of Justice

Bonus character classes
Successfully complete the indicated task to unlock the corresponding character class:

Berserker: Have a level 40 Heavy Knight and level 40 Monster Tamer.
Cheerleader (Idol): Have a level 25 Geo Master and level 25 Healer.
Female Archer: Have a level 15 Female Fighter and level 15 Female Healer.
Female Ninja: Have a level 30 Female Monk and level 30 Female Magician.
Female Samurai: Have a level 35 Female Fighter and level 35 Female Archer.
Geo Master: Have a level 20 Fist Fighter and level 20 Healer.
Gunner Female: Have a level 15 Female Thief and level 15 Mage.
Gunner Male: Have a level 15 Thief and level 15 Male Mage.
Heavy Knight: Have a level 15 Male Fighter and level 15 Fist Fighter.
Magic Knight: Have a level 25 Fighter and level 25 Mage.
Majin: Successfully complete the tutorial again on a cleared saved game file.
Male Archer: Have a level 15 Male Fighter and level 15 Male Healer.
Male Ninja: Have a level 30 Male Monk and level 30 Male Magician.
Male Samurai: Have a level 35 Male Fighter and level 35 Male Archer.
Masked Hero: Have a level 45 Thief and level 45 Gunner.
Monster Tamer: Have a level 15 Female Fighter and level 15 Fist Fighter.
Ninja Female: Have a level 30 Female Fist Fighter and level 30 Mage.
Ninja Male: Have a level 30 Male Fist Fighter and level 30 Mage.
Shaman: Have a level 25 Geo Master and level 25 Mage.

Bonus guest characters
Successfully complete the game, then complete the indicated map to unlock the corresponding character:

Asagi: Extra map 4
Axel: Extra map 6
Laharl, Etna, and Flonne: Extra map 7
Marona: Extra map 5
Master Big Star: Extra map 1
Prism Red: Extra map 3
Salvatore: Extra map 2

Alternate endings
Successfully complete the indicated task to unlock the corresponding ending:

Almaz : Win stage 8-4 with Almaz alone then the following battle.
Human World : Kill at least 99 allies and complete two alternate stages by stage 7-6.
Laharl : Go to the homeroom, propose "Watch a New Ending", and complete the stage.
Mao's Ambition : Complete stage 1-9 on the second or higher cycle before stage 4-4.
Normal : Do not qualify for any other ending.
Raspberyl 1: Lose against Raspberyl on stage 1-5.
Raspberyl 2: Lose against Raspberyl on stage 2-1.
Super Hero : Defeat the final boss with Mao at level 500 or higher.