A port of the PSP version, this includes multiplayer gameplay and Etna mode. In order to fully utilize the Nintendo DS' capabilities, several key improvements will be made to the user interface and game system. However, many features from the PSP edition were dropped, including the option to toggle between English and Japanese dialogue, and many additional voiceovers, probably due to the limited storage capacity of the DS game card.
The Nintendo DS version contains the following features:
Geo Cubes – From the PSP version, Geo Cubes are magic items that add more depth to multiplayer battles. They can be used to enhance abilities, summon monsters, or to attack the enemies.
Demon Gadgets – Randomly generated items that appear on the battlefield. Units can power up by acquiring these gadgets. Some demon gadgets can level up a unit by 30 levels at once.
Unlockable Characters - As well as the unlockable characters from the original Disgaea, Adell and Rozalin from Disgaea 2 are unlockable as hidden bosses within the Cave of Ordeals, as well as the Dark Assembly guide, Pleinair. Overlord Zetta also debuts as an unlockable, playable character.
Source: Wikipedia, "Disgaea: Hour of Darkness", available under the CC-BY-SA License.