Rayleigh’s nickname, Mei-Ō (冥王; lit dark king), is the Japanese word for Pluto/Hades, the god of the underworld in ancient Greco-Roman mythology.”
According to Wikipedia, “After their victory, according to one famous passage in the Iliad (Book XV, No. 187 – 93), Hades and his two brothers, Poseidon and Zeus, plotted to rule the kingdoms. Zeus received the sky, Poseidon received the seas, and Hades received the underworld, the world not The visible to which the souls of the dead go after leaving the world and anything underground.”
So it could refer to how Rayleigh and Roger split their rule, Roger is the pirate king and captain, and Riley is the king of darkness and vice-captain. One operates and rules in the shadow of the other in the “world of the unseen”.
You just went down a rabbit hole in Greek mythology and guess what! Poseidon is not only the god of the sea, he is also the god of earthquakes! Could Whitebeard be Zeus Roger’s Poseidon and Riley’s Abyss? Zeus is the king of the gods, Poseidon rules the sea, Hades rules the invisible world, three equal brothers split by the luck of a tie.
After further digging into the war that made Zeus, Poseidon, and Hades, the new rulers were against their father, Cronus.
Cronus came to power, as commander of the Titans, to overthrow his father Uranus known in Roman mythology as Caelus or in Celestial English. We quote from an article on Kronos: “After sending Uranus, Kronos re-imprisoned the Hecatoncheires and Cyclopes and set up a dragon camp to guard them. He and his older sister Rhea took the throne of the world as king and queen. The period in which Kronos ruled was called the Golden Age, since at that time people did not need into laws or rules; everyone did the right thing, and immorality was absent.”
Now what do we know about Rocks D. Xebec? He led a group of monsters (Titans?) against the Celestial Dragons in an attempt to become the King of the Realm, but Roger (Zeus?) stopped him in the Valley of God.
* theory bitter