All of the universe has been combined into one and one person from each universe has a crystal. Whoever gets all of the crystals gets to go back home and the rest of the universe has to wait 20 more years until the crystal reapers.
100 years after Steven saved the world, most of the gems had left and stayed on homeworld, but the crystal gems had to still protect their home
Yet 2000 years later they had seemingly vanished of f the face of the planet, those who had knew them had already died and stories quickly became myths
Until one boy decided to become a hero