I mainly want to know this because of this one headcanon I have: Kirby was originally from the Rainbow Islands, though often visited the "main land" of Dream Land, and eventually moved to said "main land" (where his house is now). I also believe that the Animal Friend characters, or at least Rick, Kine, and Coo, are from there too.
However, I don't really know if anything contradicts that, especially since the information on the Rainbow Islands that we have is... limited, due to their lack of relevance after Dream Land 2.
Anyone got anything?