The Cosmos: The term "Cosmos" refers to the Multiverse in which the Nippon Ichi Verse is set. There are an infinite number of Macrocosms that constitute the Cosmos.
Macrocosm: Each Macrocosm encompasses three distinct planes of existence: a human world, a Netherworld, and a Celestia. Each of these planes is a self-contained area of space and time. Every one of these universes can accommodate fifth-dimensional beings, such as Baal, who has been canonically stated to regard "The fourth dimension as nothing to a Super Overlord."
The Netherworld: The Netherworld is the realm inhabited by demons. Most Netherworlds are chaotic due to the inherent nature of demons, with constant battles to determine leadership. Whoever defeats a Netherworld's Overlord becomes the new Overlord. Netherworlds are generally less advanced, with many having very limited technology, although there are exceptions.
Demons derive power from an energy called Fear Energy, which is generated when a human fears a demon.
There are various types of demons including those resembling humans, dragons, slimes, wolves, cat-girls proficient in Hokuto Shinken, succubi, imps, and zombies. Besides demons, a few angels visit the Netherworld, mainly for monetary gain, and Prinnys, who work there to atone for their sins.
Laharl’s Netherworld: Laharl’s Netherworld, the main setting of the first Disgaea game, was initially ruled by King Krichevskoy until his death, after which his son Laharl took over the reigns.
Veldime: Veldime is the main setting of Disgaea 2, a once peaceful world that undergoes a transformation into a Netherworld due to a curse. As the characters battle to restore Veldime to its former state, they encounter a host of demons, challenging battles, and comedic scenarios typical of the Disgaea series.
Nether Institute Evil Academy: The Nether Institute Evil Academy serves as the primary setting in Disgaea 3. It was governed by Mao's father until his demise, after which it operated autonomously until Mao assumed control. This Netherworld is unique because it is entirely structured as a school, comprising the Freshman Building, the Sophomore Building, and the Senior Building. Despite its educational facade, attendance is scarce as adhering to goodness labels one a delinquent, while engaging in misdeeds earns the title of an honor student.
Celestia: Celestia is the realm inhabited by angels. Unlike Human Worlds or Netherworlds, Celestias are quite similar to one another, primarily because most inhabitants are angels, who are generally uniform in nature. This is in contrast to the Netherworld, with its wide variety of demons, and the Human World, populated by different types of humans, talking animals, and witches.
Angels derive power from an energy known as Awe Energy, generated from the faith humans exhibit when they pray to God or angels. Angels possess a unique physiology, rendering them invisible and intangible to anyone unaware of or disbelieving in their existence.
Celestia is consistently depicted as technologically advanced, with capabilities such as developing a bomb capable of annihilating several universes, constructing giant robots that can lift the Moon, enabling multiversal travel, and creating a digital multiverse.
Besides angels, Celestia also hosts Prinnys, who work there much like they do in the Netherworld. Additionally, demon monsters are kept as guard dogs and pets by angels to protect Celestia in case of emergencies.
Our understanding of Celestia is limited, as only two distinct versions have been depicted, compared to the hundreds of Human Worlds and Netherworlds showcased throughout multiple series.
The Human World: The Human World is the realm inhabited by humans (as the name suggests). Despite its name, the Human World refers to any universe where humans are the primary residents. Typically, Human Worlds are depicted in one of two ways: either resembling our own historical settings with the addition of accessible magic, or as futuristic realms where advanced technology aids humans, especially if they are physically less robust than angels or demons.
Contrary to what one might assume, humans can be incredibly powerful, with highly trained individuals capable of matching the might of formidable angels or demons. However, many humans utilize suits that amplify their power, enabling them to contend with demons effectively.
The Carnage Dimension: The Carnage Dimension represents another infinite set of Macrocosms, running parallel to the infinite set of Macrocosms where most of the series unfolds, collectively constituting the other half of the Cosmos. The spatial structure within this half of the Cosmos, where the Carnage Dimension resides, mirrors that of the other half, with Netherworlds and Human Worlds retaining their characteristics across both halves. The Carnage Dimension is distinguished by housing the mightiest demons, where even the weakest among them possess higher-dimensional power. This is notably significant when compared to Killia and group, who, having defeated the Fifth-Dimensional Baal, now possess the capability to annihilate this half of the Cosmos.
The Overlord’s Room: An Overlord's Room is a dimensional space that Overlords can create, and only beings as powerful as an Overlord can enter this space, as weaker beings wouldn't even be able to exist within it. From this dimensional space, individuals can observe the Cosmos through a TV, suggesting that it exists on a higher plane of existence compared to everything else in the Cosmos. This is presumably why only beings with Overlord-level strength can exist within it.
Baal: Baal is the Super Boss of the Disgaea series, among other games, and is a demon Overlord who is consistently touted as one of the strongest Overlords. His mere existence is described as Fifth-Dimensional, with the phrase: "The fourth dimension is nothing to a Super Overlord." Baal has the ability to survive all encounters, even death, by transferring his soul into other bodies, or multiple bodies simultaneously. His soul is unique as it comprises numerous evil souls and possesses omnipresence, enabling it to inhabit another body upon his defeat. Additionally, Baal is accompanied by machine-like crystals that fight alongside him, as well as powerful demons.
Overlords: An Overlord is the ruler of a Netherworld, a title typically determined by who is the strongest in the realm. Overlords are generally depicted as being stronger than other demons.
Overload: An Overload is a special skill unique to the individual possessing it. It can encompass various abilities such as time manipulation and power theft. However, one doesn't need to be an Overlord or even a demon to gain an Overload Skill; they just need to possess strength comparable to an Overlord. This has been demonstrated by characters like Zeroken, Goldion, Desco, Flonne, and Etna.
Prinny: Prinnies are a race found across the Cosmos, comprising sinful humans whose souls have been placed into Prinny bodies. They are subjected to grueling labor to atone for their sins. Once their sins are paid off, they can be reincarnated into another body. In rare instances where no Prinny bodies are available, the individual will don a Prinny-themed hat and jacket, becoming what is known as an Unprinny.
Evilities: Evilities are akin to abilities in Pokemon, providing a passive bonus or resistance to the holder. They are categorized into two types: Unique Evilities, which are specific to an individual (unless certain requirements are met), and Common Evilities, which anyone can possess. Most Evilities either boost a person's stats or provide resistance to various elements.
Innocents: Innocents are living entities residing in a realm known as the Item World. They exist solely within items, enhancing the items with stat boosts, passive abilities, and resistances. Within this realm, Innocents take on the forms of Demons, Angels, and Prinnies.
Mana: Mana is a natural life force used to gauge a person's strength. It can be accrued similarly to EXP through combat, although some individuals naturally possess more mana than others.
Skills: Skills are special moves individuals can utilize. They are categorized into four types: Unique Skills, which are exclusive to an individual; Weapon Skills, which can be used only when wielding a specific type of weapon; Job Skills, which are accessible only to demons of a certain class; and Monster Skills, which are exclusive to certain types of monsters.