@Kirk:
The thing is, it would imply the winged people to create both the poneglyphs, the devil fruits, the will of D, and ancient weapons. Pretty hard if you ask me. Have we seen evidence of such powers in Skypiea?
Poseidon is mentioned on a Poneglyph in Skypiea, and they created Dials, so they certainly could have had the ability to make Devil Fruits.
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@Jackermeister:
I'll take that as a yes.
I refer to Robby Bevard.
@RobbyBevard:
The theory comes from the Skypeia arc and the Enel cover story and a whole messload of other minor details that have been debated constantly for years now. Luffy with the wings winking on the volume cover is taken as an additional hint, but its hardly the one piece of evidence. (see what I did there?)
The winged people are from the moon.
They came to earth.
Some mixed with a race of 'unwinged' individuals from below. Incredibly likely, given the glyphs Enel saw that demonstrated multiple different winged peoples.
They founded Shandora, part of the giant kingdom and lived in peace until SOMETHING happened. No clue as to what yet.
Sky Islands are reachable, but so rare and difficult that its largely believed to be myth.
Known D.'s have varied in size and even species, from human, to large-scale human, to giant. Whitebeard commented there was specific D that had been "waiting for", and Blackbeard was not it.
Shandora's destuction times out exactly with the void century.
Luffy is wearing a set of wings on a cover and winking at the audience.
Add to that the nearly certain theory that One Piece is the poneglyphs and true history, (it may also have piles of gold, but that's secondary) and that upon discovering the truth, Roger's crew, according to Rayleigh "were unable to do anything to fix it"… and that Roger's capture was, we now know, planned on his part since he was dying anyway, and Roger's entire goal was to encourage others to do what he could not.
We also know that one of the ancient weapons was a mermaid princess that summoned seakings, one was a giant ship (the designs of which happened to be in the hands of a fishman!) and that the government has been buiding a bridge for SOME reason for 700 years, and the fact the world government has been set up in the story thus far as in serious need of a toppling...
The D's were wiped out in a major THING during the void century. But a few specifically survived and wrote down the story and hope to some day be avenged. Their decendants will eventually carry out their will and topple the corrupt government built upon their slaughter.
Theory-The individuals who carried the traits of both moon individuals and people of earth at some point came to be designated as 'D.'. Whether this was a derogatory term or a term to secretly express connection we can't tell, but they were labeled for a reason. The meaning of the 'D' is simple in that it represents precisely what they are, HALF moon, not the alphabet 'D' but in fact a pictogram for half of the moon. As the alphabet came to be used, it was lost as a 'D' instead of a pictogram. This is why Luffy is winking on the cover with wings, because he carries the 'half' blood himself. Now, we've never seen evidence that he actually had wings so he might not be a 'half' but the point is, those individuals carry those genes and the D is a way to identify them.
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@Kirk:
They did not create dials, these stuff come from shellfish that have the ability to store the energy. They just perfected it. As for Poseidon, I don't see your point. Pluton was mentioned in Alabasta, so?
It's hard to discuss with you Kirk, after I show you proof you use a completely different example to deter it.