Universe of Kingdom Hearts - Worlds

Worlds

In the Kingdom Hearts universe, travel between worlds is not normally possible. Worlds are protected from extraterrestrial interference by an invisible shell. When the heart of a world is opened, the shell breaks apart, appearing as a meteor shower. Fragments from the wall are called "Gummi blocks" and can be used to make spaceships called "Gummi Ships", which serve as the main mode of travel between the various worlds. Gummi Ships can be shaped into any structure, and the origin of the Gummi Ship material allows for travel to other worlds. Gummi blocks can serve different functions, from navigation to offense and defense. Other methods to travel between worlds are the "corridors of darkness" and the "lanes between"—interdimensional pathways through which frequent travel eventually erodes the user's heart with darkness. These pathways are normally used by Heartless and Nobodies, but have been used by other characters in the series, including Riku and Mickey Mouse.

Those who travel between worlds are advised to limit their interactions with the inhabitants of foreign worlds in order to maintain the world order. For this reason, the main characters change their appearance in certain worlds to avoid standing out. In the worlds based on The Little Mermaid and The Nightmare Before Christmas, Sora, Donald, and Goofy transform into undersea creatures and Halloween monsters, respectively. For The Lion King, they transformed into animals (or, in Donald and Goofy's case, less humanoid forms) because Nomura felt that it would appear odd to have Sora and the others interact in their standard forms, since no humans appear in that film. Also for the Space Paranoid world in Kingdom Hearts II Sora, Donald & Goofy are transferred into data and have grey armor with blue designs, much like the recurring character for that world, Tron.