Eternia is a central planet in the Masters of the Universe franchise.
Magic gave birth to Eternia, the first planet in all of creation, the nexus of all space and time. The Sword of Power was the artifact that binded that magic to Eternia. When the sword was split in two, it returned to the realms in which each half was formed: Preternia and Subternia. Without the sword, all the magic on Eternia began to fade and the planet began to rot and die. The end of Eternia would mean the end of the entire universe.[1]