My lovely gem!AU 
I think here is a little different story, suppose that there was no war and almost the entire galaxy captured Purple Diamond (Zarkon) and from under his yoke fled rebel group. Who settled on a habitable planet Earth. Planet is a new purpose Purple Diamond. There they meet little girl Allura. They settled in her house and develop a plan for PD
(and alco, Allura really like fusion Klance)