Absurdity

The First World

• * There were no devil fruits to start.
• * There was a very advanced civilization.
• * They possessed nuclear technology or a greater equivalent.
• * "Fire on the earth because they touched the forbidden sun" They destroyed the land with their technology.
• * Despite being advanced this civilization either kept or allowed slaves to be kept, or possibly this is after the initial destruction of the land and their society has already collapsed from the fire on the earth, the destroyed land from their technology. These slaves prayed to the god of the sun. A god of freedom and destruction. Now theory time, I think this sun god was a real person, akin to Vegapunk. They are the God of the technology, perhaps at odds with the current government after listening to the people, or if no government just a bit reckless in their help. This can all be a bit symbolic, some may consider Vegapunk a god by his technology. It is in quotes because he is not a true god, but someone they might look up to. During their war for freedom he likely fought irresponsibly and the earth god became enraged. This could also be a metaphor for the destruction being caused.
• * Either the other side or a third party unleashed the world serpent that ate up all the land. Or even the sun god as part of their attempt to help at first if they were like Vegapunk, master of technology. Perhaps it started as an experiment to restore the land, but ended up eating it all and got bigger and bigger (why it is a snake made of earth, perhaps nano tech). Eventually this "serpent" was stopped or it stopped itself when it ate up enough land to form a full circle around the planet, dividing it and taking most of the land with it. This might be how the continent disappeared, all the land was made "sentient" or alive, a true "world" serpent, made of the world.

The Second World

• * I think the god of the forest could mean another scientist, someone who created the devil fruits. Maybe someone from Elbaph as well, or at least did it on the island. It could relates to the Adam tree, that was where the fruits originally grew from then spread elsewhere to re-grow through their own will. This is when devil fruits came into existence. Perhaps this was Imu, or a connection with Imu. This likely happened a while before Joy Boy came around, he was born into a world where Imu was not in charge, but taking hold.
• * The sun spreading embers of war is Joy Boy going around starting to bring forth the call to freedom again, with the Nika fruit, which was built on a dream of Nika, an ideal. At this point in the second world the first world would be a myth. They wouldn't really know what Nika was or wasn't. They created this version of him into a fruit, that will, where in reality the original Nika could again have been very different or a metaphor. Joy Boy was likely trying to create resistance to the rising tide of Imu, gathering "embers" for a war, but they were just embers, he never finished lighting the sun.
• * The people of the moons dreamed. These were likely people left over from the first world, trapped on the moon(s) when the first civilization collapsed. Through their dreams they created more devil fruits, or exerted their will onto the fruits. It feels like they had different dreams or goals, with the half moon being destroyed and wiped from existence, perhaps this was the heir to the ancient kingdom Imu saw as their enemy. The people of the other moon perhaps sided with Imu, or at least at first, centuries can change things.
• * Dreams can see into the future, perhaps even create or shape it. Might be why Imu was so intent on destroying the half moon people, and then the moon people more slowly, to destroy their dreams would be to stop the future they could create. Can't kill the dreams, but killing the dreamers could perhaps kill the dream out of existence. Why after Joy Boy was killed he wanted the Buccaneers gone. Perhaps Imu thought they would forget, but after a few 100 years the dream still gets passed down.
• * Humanity killed Joy Boy. Not Imu. He was betrayed, perhaps he was led into a trap, or waiting on friends to come to a fight who never did. It seems likely that they were allied with the 20 kingdoms who became celestials. To do Imu's bidding they came together and fought him in a war, and tricked his allies into not helping or pretended to be allies before attacking.
• * During this battle the grand line and the calm belt were created. It may have been Imu's doing, or a consequence of the weapons they were fighting with.

The Third World

• * This is the age we are currently in.
• * Void upon the chaos, means the Second World, or the end of it, was chaotic, and the creation of the void century to hide that and create order.
• * The talk of the promise is the promise Joy Boy made to the world. Luffy will fulfill this promise and turn those embers of war into a full on fire of solar inferno.
• * The voice of the fragmented moon, the half moon people, perhaps the voice of all things, this voice lives on and the unbidden shadows represent those with the D and the sea beasts.
• *During this war/battle Luffy will destroy the red line, and Fishman Island along with it. The grandline will also be destroyed and the whole world will be united once again and they can all celebrate together.
• * Luffy's reality warping powers may be key to this, but to warp the whole world at once may require a self sacrifice.
• * Luffy returns with a new dawn, or perhaps an embodiment at least, his spirit as the world celebrates the way he would have wanted. Perhaps his spirit is part of the world itself now, and everyone can feel his warmth as we enter the fourth world at the end of the third.
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• Another possibility is looking at the image the final battle doesn't seem to be against Imu, but someone trying to steal the sun with a pirate ship on their side. This is likely Blackbeard, after Luffy wins against Imu, Blackbeard will come in and steal the sun, Luffy's fruit. I think this is where Luffy "dies" at the end of the third world. Everyone will unite against Blackbeard and return the sun, Luffy(?) or just the fruit, bringing in a new dawn.

All this and I still have no solid guess as to the One Piece treasure. It is likely a funny story that can make the world laugh, perhaps of Imu, and contains the world history. Knowing the true history of the second world the Roger pirates would realize they need to start a slow burn to get the world against Imu. Letting them know Laugh Tale and the One Piece are real would be a blow that would grow and spread all over until someone could come across with the power to awaken Nika's fruit. They were too early, because they needed someone with that fruit awakened to start the final war. Perhaps the one piece is key to healing the red line and the grand line when aligned with Nika's full power. It could likely be great technology left over from the first world, the ultimate power to shape the world itself. Perhaps the ability to create more devil fruits through dreams.

I kind of feel that Laugh Tale is the moon, or the remains of the half moon. They will have to find a way to go into space, which may be possible now that they have Vegapunk as an ally. The last island before Laugh Tale is supposed to be Lodestar, which I think will help guide them to the "stars" (the moon) and the remains of the ancient kingdom that is on there.