After a two-year sleep, Prince Laharl awakens to find his father, King Krichevskoy, dead and the Netherworld in the middle of a civil war over who takes the throne. Not willing to give up his rightful place as the next king, Laharl joins with his subordinate Etna and her underlings to fight back.

The Overlord's castle acts as a hub to manage the party. It has shops to get new equipment, a gate to the different battles, a NPC to travel to the Item World, which is used to boost items, and the Dark Assembly, where the player can create new units, and have the assembly vote to pass (or not) special laws that will affect the game. To unlock some characters, a special chapter must first be unlocked by the Assembly.

The story progresses in the form of chapters. In each chapter, new battles become one after another, with dialogues at the beginning and end of those battles. Any completed battle becomes available to play again, sometimes with minor changes. At the end of every chapter, a parody cut-scene announcing the next chapter,(most often, it is Etna who tells the story as if she were the protagonist) is shown.

Battle In a similar style to Final Fantasy Tactics and Ogre Battle, Disgaea is a turn-based strategy RPG on an isometric grid. Characters are dispatch in battle one after another, and each have a move action and an battle action. Each class has its own set of abilities, ranging from simple attacks and area attacks to magics that can affect all the battlefield. In each battle, up to ten bonuses can be obtained by clearing the Geo Panels and defeating enemies to fill the Bonus Gauge. The battle is won when all enemies are defeated, or, in the Item World, by accessing a gate to move to the next floor.

The Item World The Item World is a world divided in floors, inside any of the player's item. The goal of the Item World is to progress through the floors, which raises the item's level. The more enemies are defeated before moving to the next floor, the more the item will improve. A special king of enemies, Residents, can be found in the Item World. These have their own level, and add a bonus to the item in which they reside. Once a Resident is defeated, it is "subdued", its level doubles and it can be moved between items. Residents can be fused together to get better bonuses. This is necessary because each item has a maximum number of Residents it can contain, determined by the item's rarity (common, rare or legendary).