this is why coco’s house looks like a pyre, for some of these figures the body would be cremated and the ash mixed with clay to create the statue
her japanese name is also Yayoi which is a reference to the japanese yayoi period which is when the haniwa statues that eventually inspired gyroids came about
so coco is more like. a ghost possessing a statue.
here are some japanese haniwa figures from the kofun period that more closely resemble the in-game gyroids ( note the arms! ). the rain’s part in this was mostly, like with any other shallow grave, loosening tge earth around them and washing it away, allowing it to eventually work its way up to the surface.