Long ago, near the dawn of a new time, Ninjago was created by the first Spinjitzu master. This master, had the power to wield all four elements at once and with these elements, he had defeated an ancient evil, known as the Overlord.
But what no one on Ninjago knows, is that he wasn't the first, and that there were more elements involved in Ninjago's creation. This first master was one of many, known as the Mulematra. People, with the courage and sacrifice of Fire and Earth. Tranquility of Wind, Water and the Oceans. Intelligence and wit of Lightning and Ice, all a part of one single being.
Has no one brought to question where the "First" master came from? In old legends, among those of the Great Devour, Ninjago's separation, the Serpentine people and many more, is the legend of the Elemental Isles. And it is these Isles that the first master was born on.
It is said that only a few are chosen to enter these unknown islands. Only those with a physical, mental and spiritual connection to their ancestor's element are allowed to enter back home. But once you are in, it is very rare that you come back, and those who do come back, have lost a great majority of their memories of these Isles, and who were on them.