I think Loki is the reincarnation of the Earth God, just like Shirahoshi is the reincarnation of the Sea God (Poseidon), and that they are the two kings destined to meet again.
The destructions described in the Harley during the First World and Second World turned what was once a united and peaceful world into one defined by destruction and separation. The role of Nika/Joyboy/Luffy is to reunite these two kings and the world itself.
The One Piece is sometimes referred to as Hitotsunagi no Daihihō, the “"the incredible hidden treasure that connects people".
I believe that the “Earth God” mentioned in the Harley wasn’t the original ruler but an usurper, a figure similar to Enel, someone who enslaved entire populations to extract resources from the rich continent that existed at the time.
The creation of the Red Line was the first great cataclysm that shattered the world. The second was the rising of the sea level. Across the different Worlds, the two figures who are unable to meet are always Poseidon and the king of the ancient giants, possibly characterized by the distinctive eyes we see in Loki.
Roger reached Laugh Tale too early because the two kings, Loki and Shirahoshi, had not yet been born.
These are figures that seem to be reborn every 800 years, and the world has been waiting for their reunion.
It’s no coincidence that Fishman Island and Elbaph share strong connections. The Adam Tree in Elbaph and the legendary Tree Eve, whose roots reach all the way down to Fish-Man Island to provide light and air to the ocean floor, are one of the clearest examples.
During the Fishman Island and Elbaph arcs, we saw Loki and Shirahoshi both deprived of their freedom. It was Luffy who set them free, the person who will eventually reunite them.
As a side note, I think each of the three Worlds is defined by the presence of a negative figure, an usurper who embodies sin, greed and the thirst for power.
In the First World, I think it was a figure from the Moon, someone who came to Earth in search of resources and enslaved humanity.
In the Second World, we have Nerona Imu.
In the Third World, the one that I like to call the final villain of One Piece @Fujishiro @Paperchampion23 @Loki D. Terror
Darkness. The black hole. The abyss that devours everything. The only true king of the world...
