For many years, a large part of the One Piece fandom (including me) believed that Oda had achieved something almost beyond human capabilities: developing a frame plot (concerning the great treasure One Piece, the great powers of the world, the poneglyphs and the void century) at the very beginning of the story, making only minor adjustments to it as the story progressed.
That is to say that we believed that Oda knew the most important details of where the story was going as early as Chapter 1, or the East Blue saga at the latest.
In more recent times this belief has been called more and more into question. The mere fact that the story has stretched much beyond what was originally planned makes it unlikely that the complex frame story that has unfolded in the recent years was entirely devised at the beginning of One Piece. In addition to that, though many believers will deny it, the second part of the story (after the TS) gives off strong hints that the frame plot is deviating from the original plans (particularly with the surprise revelations of Nika and Imu, which according to many were not prepared well enough from a storytelling point of view).
An alternative, minimalistic possibility is that when Oda started publishing this story he had no clear idea of where his story would head, and perhaps he didn't even know what the great treasure was going to be, and what would be achieved by finding it. However, Oda stated that the end of the story, with the main characters finding the One Piece, has never changed in his mind. There is no reason to doubt Oda's words, but most importantly I don't want to doubt them because it would be really unappealing if we had been reading for decades a story whose goal wasn't clear even to its author.
So, it's possible that the truth lies in the middle: Oda has always had a solid idea of how the story was going to end, but the frame plot has been evolving during the years, as a set of nested shells around that main idea. The inner shells were devised closer to the beginning of the story and we have had such a long time to process them that we don't even see them as a patch to the story; but sometimes the outer shells, which maybe have been added after the midpoint of the story, do feel less solid than the rest of the plot.
So, I want to propose a game: to reconstruct the order in which Oda first devised the various elements that make up the frame plot. I'm going to start with a few of these elements, but surely there are many more.
Romance Dawn arc
-
Establishes that Gold Roger, the Pirate King, was the man who achieved more than anybody else.
-
Roger was put to death, but he left his great treasure, the One Piece, in a certain place, for a new generation of worthy pirates to find it.
-
The protagonist appears: his name is Monkey D Luffy
-
Haki (colour of the conqueror) is shown for the first time (though the theory of haki presumably hadn't been developed yet)
-
Koby mentions that to find the treasure, Luffy must head to the Grand Line.
Orange Town arc
- First appearance of Silvers Rayleigh (in Buggy's flashback, unnamed)
Baratie arc and Arlong Park arc
- First mention of the Three Great Powers of the Grand Line.
- One of the three great powers, the Shichibukai, is a group of seven pirates who made an agreement with the World Government; they include the world's strongest swordman Mihawk and the leader of the Fishmen Pirates, and Arlong's ex boss, Jinbe
- Vice Admiral Garp is introduced in a cover story
Loguetown Arc
- The named swords and their hierarchy are introduced, including the three Kitetsu swords
- Dragon is established as a wanted man and a powerful figure
Reverse Mountain Arc
- First appearance of Crocus
- Explanation of the logpose and navigation in the Grand Line
- First mention of Laughtale as the final island of the Grand Line
Whiskey Peak arc
- Crocodile is introduced as a member of the Shichibukai
- First mention of Alabasta. Vivi is retconned (according to Oda's statements) to the princess of that country.
Little Garden arc
- First mention of Elbaf
Drum Island arc
- First mention of the Will of D
- Roger's real name is revealed to be Gol D Roger
- First (unnamed) appearance of the Blackbeard Pirates
- The Levely is shown in a flashback; Dragon is described as a revolutionary and the world's most dangerous man
Arabasta arc
- Poneglyphs and the true history are introduced. The stone located in Alabasta contains information on the location of the ancient weapon Pluton
Jaya arc
- The (presumed) highest authority of the World Government, the Gorosei, make their first appearance
- More world-relevant characters are introduced, including the shichibukai Kuma and Doflamingo and the head of the Marine, Fleet Admiral Sengoku
- Blackbeard is established as Luffy's nemesis, and his name is revealed to be Marshall D Teach
Skypiea arc
- colour of observation haki makes an early appearance in the form of mantra
- two groups of winged people (Skypieans and Shandians) appear for the first time
- Robin discovers a second poneglyph, explaining the existence of another ancient weapon called Poseidon
- Gol D Roger somehow was able to write a message using the poneglyph code (this was later revealed to have been written by Oden, though it is questionable whether this character had already been foreseen by Oda at this point)
Longring Longland arc
- First mention of the three Marine Admirals, and introduction of Admiral Aokiji
(to be continued...)