Essence is the fundamental force that constructs the world, the Nine Heavens, and the Nine Hells. It originates from an unknown entity, one so mysterious that even the most powerful beings have failed to uncover its nature. Every action performed by living beings relies on the circulation of essence within their bodies.
To complete this circulation, living beings are born with an essence core — a natural vessel that forms shortly after birth. However, there are rare exceptions. It is said that the strongest beings transcend the need for an essence core altogether, their mastery of essence so profound that they manipulate it freely without a medium. Conversely, some unfortunate souls are born without an essence core at all. Known as "Hollows," these beings are fated to perish soon after their birth, unable to sustain their existence.
At the pinnacle of power stand the Emperors of the Heavens and the Emperors of the Hells, along with their elite vanguards. The Nine Heavens are named after southern and southwestern constellations of Earth: Hydra, Carina, Orion, Monoceros, Vela, Mensa, Hydrus, Virgo, and Aries.
Opposing them, the Nine Hells draw their names from the constellations of the eastern and northern skies: Canes, Ursa, Coma, Crater, Corvus, Draco, Volans, Cygnus, and Musca.
The Heavens and Hells are locked in an eternal struggle for dominance. Secret wars rage in the shadows, assassination attempts against key figures are common, and shifting alliances constantly reshape the balance of power. Internal conflicts within factions further fracture the stability of both realms, often spilling into the mortal world and altering its very structure.
The connection between the mortal world and the higher realms exists through pathways — vast rivers of essence controlled and guarded by distinct factions from either Heaven or Hell.
Among ordinary people, the existence of the Emperors remains shrouded in mystery. Only the highest-ranking bureaucrats, soldiers, and those who serve directly under them know of their reality. For the vast majority, their existence is mere rumor, whispered myths without tangible proof. The Emperors themselves remain detached from worldly affairs, indifferent to the struggles of the common world.