Vegapunk reveals that Joyboy was a man from the Great Kingdom, born 900 years ago at the start of the Void Century, and was the first pirate in history.
I believe that Imu would have join forces with 20 kings to defeat Joyboy. They destroyed Joyboy’s ship in the war but couldn’t burn his Jolly Roger. While the ship was destroyed, “one piece” of it remained, symbolizing everything pirates live for. This is why Imu and the World Government hate it and are doing everything possible to keep it out of the hands of today’s pirates.
During the run up to Laugh Tale, maybe the Straw Hat Pirates Jolly Roger might be damaged by the World Government. When Luffy returns from Laugh Tale, he could be flying Joyboy’s Jolly Roger alongside his own, much to the frustration of Imu and the World Government. This could become a unifying flag for the entire alliance against the World Government during the final war.
Since Luffy has inherited both Joyboy’s fruit and his will, if Joyboy designed his own Jolly Roger, it might be as wacky as the original one Luffy made. This could explain why Roger laughed. Also, Roger might have laughed because he spent so much time thinking he would be the first to discover the final island, only to find someone else’s Jolly Roger there.
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