Now the question is if Imu is the original earth god or a vessel like Luffy is to Nika, that is open for interpretation. I think Imu was born in the secon world and inheritted the earth god's powers.
Watch bro. Imu is a tragic figure, a pure hearted child like innocence turned into an unspeakable evil out of fear. Imu is more akin to a scared and terrified child than an actual demonic overlord.
Joyboy and the ancient kingdom were the science guys who had carved out a living for the diverse moon origin? races on earth but as their science advanced they came close to destroying (with or without intent) the earth with the powers of the infinite energy source aka forbidden sun aka nuclear energy.
The more I read the text describing the third world the more I'm confident that it's way more about Teach than Imu.