So, in this universe, Magnifico was once the royal alchemist for a wealthy kingdom. Wanting to become the most powerful being alive, he created a spell that would steal peoples' heart's desire. Not their wish necessarily, but their taste for life and their ability to wish for themselves.
He started using this spell on the kingdom's people, leaving them lifeless husks. He promised that he would eventually give everyone their life force back and that they would more alive than ever before, but the people hadn't gotten their heart's desires taken realized that he was lying. They revolted against him and gave the life forces back to the people, but an outraged Magnifico burned down the entire kingdom.
After hiding out for years and growing even more powerful, he created Rosas, and he used the rebellion as evidence for why people should submit to him.