Disgaea D2: A Brighter Darkness is the sequel to Disgaea: Hour of Darkness. Prince Laharl has now become the Overlord of his own Netherworld, but is lacking charisma to gather many vassals and be recognized as such. The Krichevskoy Group, a gathering of Laharl's late father's former vassals opposes Laharl's Overlordship. When Yuie, flowers native to the angel's realm Celestia start appearing in Laharl's Netherworld, strange events affecting demons start occuring: Etna changes colors and now look like she is "Player 2", the early bird Flonne starts oversleeping, and Laharl himself wakes up as a woman. Only the angel Sicily, who claims to be Laharl's sister, is unaffected. The Krichevskoy Group blames Laharl for the appearance of the Yuie flowers and those incidents.

The game takes after its predecessors for most of the gameplay elements, including the turn-based battle grid: party units are dispatched on an isometric battlefield from the base panel, each having one move action and one battle action each turn. The range of those actions depends on the character's stats and class, and on which ability is used. Performing combined attacks and destroying the Geo Symbols found in certain battles raise the Bonus Gauge. Up to ten bonuses including experience, HL and items are rewarded depending on the level of this gauge (ranging from 1 to 10) at the end of battle. One of the series's key feature, throwing, has been tweaked to allow throwing units withing a circular range rather than only on four sides.

The world hub is the Overlord's Castle, where Laharl will gather his vassals to gain more power and find out what is happening. Like before, Humanoid and Monster units can be created (or reincarnated) from the Dark Assembly. Those units now have some customization options, such as a choice of palette and a personality that defines the character's voice and Evility (a special class-dependent passive ability), which can still be changed once the unit is created. The voice and Evility can be changed independently even though they come together during the character's initial creation. New units such as angel warriors are now available, and the monsters can be rode on by humanoid units in battle (Monster Mounting), taking damage in their steads. This allows them to use new combined attacks. Characters now have relationships shown by a likeability scale of one through five hearts. Likeability can be increased by talking to the party members in the Overlord's Castle or by having them team-up in battle. The Item Sea (also known as Item World) returns with Mystery Rooms, Item Assemblies, as well as bonus stages replacing the Reverse Pirating events.