One of the universe's oldest races, they're credited with having a role in creating Nebla. They're best known for appearing to Soya in the form of his older brother—which reflects how they actually work. Their existence is fundamentally tied to perception: whoever encounters them sees them as the person they most want to see. It's less that they shapeshift and more that they literally appear as whatever form makes the most sense to the observer.
Content compiled by AnimeList.moe from publicly available sources.