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The Eighteen Levels of Hell, as the name suggests, are divided into eighteen layers. However, in the Netherworld, the Eighteen Levels of Hell are further divided into two parts: the Palace Hells and Purgatory. The upper nine levels of hell are called the Palace Hells, and the lower nine levels are known as Purgatory.
Before the Hell King had opened the passageway between Hell and the Netherworld, the people of the Netherworld treated the upper nine levels, the Palace Hells, as their own territory, and the lower nine levels, Purgatory, as the place where souls went after death.
The reason for this distinction is that there is a small island floating between the ninth level of Hell and the tenth level of Purgatory. At the far end of this island, there is a black vortex resembling a door.
The ancient people of Netherworld City called this vortex the Black Realm, symbolizing the terrifying end of life, where anything that entered would disappear forever.
