Oda set up everything to make Kuma’s flashback the most interesting and innovative flashback of One Piece.
Firstly, by defining Kuma’s memory bubble and making it possible for the characters to enter it and see the flashback with their own eyes, and to feel the emotions of a traditional flashback in a new and tenfold way.
Second, the culmination of the evolution of a character as complex as Kuma and the key pieces to understanding him and his motivations:
Kuma was first introduced as a Shichibukai, then made us believe to be a powerful enemy in both Thriller Bark and Sabaody, but finally saved the whole crew’s life by helping them to train and progress. He then protected the Thousand Sunny for two years, then became only a robot at the service of the government, Navy and science. Then finally he is transformed into a slave, then freed because he is part of the Revolutionary Army. Then he is the father of Bonney, etc etc.
The infos we have about him throughout the work portrays a complex and rich character, whose missing pieces of his life that can be revealed in this flashback could lead to the completion of one of the best written and portrayed individuals in the work of One Piece
Third, the context of the flashback and lore drop about the overall story:
Looking at the mini-flashback in chapter 1074 when Bonney enters the bubble, we notice several clues that could lead us to think that Kuma’s flashback takes place on a certain island that we know of and that has now disappeared.
Celestial dragons without helmets, expanses of grass, slaves with broken teeth and luxurious homes surely reserved for the owners of these slaves. Apart from the very famous Mariejois, only one place in the world of One Piece is known to have these attributes. I’m talking of course about God Valley. Kuma is 47 years old, and God Valley only disappeared 38 years ago from the present time of the story. He could therefore have been a child slave treading the land of this island.
So we come to the most interesting point of this theory: The possible encounter of Luffy’s crew with Kuma’s memory bubble. In other words, the Mugiwara on God Valley. Witnesses of a bygone era and maybe even witnesses of one of the biggest and most secret battles in history. From the expansion of the Celestial Dragons lore, through the tragic life of Kuma to the possible introduction of Rocks D. Xebec or even the vision of the crazy battle that was held on this island.
Anything is possible if the strawhats fit into this bubble. And I think that’s going to happen.
And that would be, for me, the greatest flashback of One Piece, the most innovative, revealing and tragic at the same time.
Theory by leoplanelles (https://www.reddit.com/user/leoplanelles)