The meaning of the “D” in One Piece is well-known but still leaves many questions unanswered. While we understand that the “D” represents concepts like the dawn, Nika, and the straw hat, we don’t fully grasp how this symbol was chosen, why it’s part of certain names, or its deeper significance.
Characters with the “D” are portrayed by the Celestial Dragons as literal boogeymen, depicted as monsters who opposed them. This portrayal likely stems from a past conflict where the “D” people were defeated. As Doflamingo explains, the victors rewrite history and define what is considered just.
It’s almost certain that the “D” people were either rebels—like the crew of Joyboy, the first pirate—or the inhabitants of the Ancient Kingdom, which was nearly destroyed by the allied 20 nations.
The narrative isn’t likely to be a simple contrast between enlightenment (represented by the “D” as dawn, light, sun, liberty, and knowledge) and obscurantism (with the government suppressing progress and enslaving people). As Rayleigh and Vegapunk have suggested, the situation is likely more complex.
I don’t think Imu will be redeemed, nor will Joyboy be revealed as evil. However, Joyboy’s methods might have been morally ambiguous, and Imu’s actions could be better understood in the context of his motives.