Is the strange reproductive process in The Twelve Kingdoms based on a myth or legend?
I touch on this in my answer to your other question. Eastern and Buddhist myths often use the cosmic egg to explain creation. In Chinese mythology, it is Pangu who hatches from the egg. In Hindu mythology, it is Brahma. In Buddhism, Buddha himself is depicted as hatching from the egg as seen below.



The myth of the World Tree is another that pervades religion.