Six-Faced World

The Six-Faced World (六面世界 Roku-men Sekai, lit. "Hexahedral World") is the setting where Mushoku Tensei takes place. It is a world in hexahedral form where all beings live on its planes. It exists in a die-shaped structure with a total of six faces, each face is constituted of one world ruled by one God each, with another seventh world of nothingness inside the die-structure.

History
In the un-recordable times, before the Six-Faced World was created, there existed the powerful "maker of worlds" simply known as God of Creation (創造神 - Sōzō-shin). He felt he was slowly dying and would not last for eternity, so he tasked himself to create one last world before his time was up. However, he realized he did not have enough power left to build a stable world; the new world that he had created was severely deformed and unbalanced so he decided to create yet another world. It ended up as another distorted world, nonetheless he kept going until he finished making six worlds, namely: Dragon World, Demon World, Beast World, Ocean World, Sky World and Human World, with the seventh Void World of nothingness at the center.

They were all distorted worlds which would soon collapse on its own, so The Creator stuck the six worlds together and was finally able to achieve stability. In this manner he established the Six-Faced World where each world supported the balance of the others. Still not content, The Creator decided to carefully manage the worlds until the inhabitants can settle and stabilize. With his remaining strength, he divided his body into six alter ego's and descended onto their respective worlds.

Soon after, as a result of their divine origins and diligent effort to make their world prosper, the ego's came to be respected as "Gods" by each world's inhabitants. In the Dragon World, it was called the Dragon God; in the Demon World, the Demon God; in the Beast World, the Beast God; in the Ocean World, the Ocean God; in the Sky World, the Sky God; in the Human World, the Human God. At the creation of his new six-sided world, The Creator ceased to exist and from him came the new Gods that came to be known throughout the Six-Faced World.

Dragon World
The Dragon World (龍の世界 Ryū no Sekai) is the world of dragons ruled by the Dragon God, where the sky and the land are reversed. It was inhabited by a race with enormous power. The Dragon Race were once primitive species who were not able to develop civilization due to their harsh environment and rogue dragons but that soon changed after Human God lent the knowledge of the humans to the Dragon God. The Dragon Race taught inhabitants of the other worlds how to manifest Battle Aura.

Demon World
The Demon World (魔の世界 Ma no Sekai) is the world of demons ruled by the Demon God, full of miasma and noxious mist. It was inhabited races with extraordinary physiques. Similar to the Dragon Race, the Demon Race were once primitive due to their harsh environment where demonic beasts roamed and reliance on their extraordinary bodies, but the world soon changed into an orderly style after the Human God lent the knowledge of the humans to the Demon God. The Demon Race taught inhabitants of the other worlds how to reinforce a weak body in order to use Battle Aura efficiently.

Beast World
The Beast World (獣の世界 Kemono no Sekai) is the world of beasts ruled by the Beast God, with dense forests and mountains. It was inhabited by races with keen senses and powerful talons. The Beast Race taught inhabitants of the other worlds how to capture and tame monsters and wild beasts.

Ocean World
The Ocean World (海の世界 Umi no Sekai) is a world of water ruled by the Ocean God. It was teeming with life, inhabited by races with gills, fins and scales. The Ocean Race taught inhabitants of the other world how to purify and method of storing water.

Sky World
The Sky World (天の世界 Ten no Sekai) is a world of rocks floating in the sky ruled by the Sky God. It was inhabited by a winged race who flew freely in the sky. The Sky Race taught inhabitants of the other worlds how to study and predict weather.

Human World
The Human World (人の世界 Hito no Sekai) is a world of flatlands and prairies ruled by the Human God. It is inhabited by a race with weak bodies but brilliant minds. The Human Race taught inhabitants of the other worlds about the importance of reading, writing, communal living, social order et cetera and gave the light of civilization to the races. After the fall of the other five worlds, all the survivors fled to the Human World and settled in their suitable habitats. In this manner, the Human World is now filled with a variety of Races.

Void World
The Void World (無の世界 Mu no Sekai) is a pure white world of nothingness formed when the God of Creation stuck together the six worlds in a die-structure. It later served as the connecting path for moving from one world to another as it is in contact with all the worlds. It is also the channel for summoning and teleport magic. This pocket of space is where Hitogami exists.

Trivia

 * Earth lies outside the Six-Faced World.