We know that Gol D. Roger had a straw hat in the flashback with Rayleigh.
Then Roger gave the straw hat to Shanks who gave it to Luffy.
Whitebeard knew about the “Will of D” from Roger. Whitebeard was curious about Luffy’s straw hat in Marineford perhaps because it reminded him of Shanks but maybe also because of what Roger told him about the Will of D and possibly about its connection with the straw hat.
Roger could hear the Voice of All Things and most likely had knowledge about the Void Century considering he could understand the Poneglyphs. It is unlikely that he knew about the Void Century when he met Rayleigh though when we see him wearing a straw hat considering he most likely had not awakened his ability to hear the Voice of All Things. Even if he had, he would most likely not have access to a Poneglyph in the East Blue that furthermore told about the Void Century.
It could be that it is people familiar with the Void Century that passes down the straw hat to promising D’s but maybe there is more to it.
We know that the era of the Rocks Pirates Garp talked about at Reverie was about 40 years ago before the Pirate King Gol D. Roger came into power.
In the present, around 22 years after Roger’s death, Luffy has a straw hat just like Roger and has chosen to take the same path.
This is pure speculation but if the captain of the captain of the Rocks Pirates also had a straw hat, then that would mean there is a pattern with a new enemy of the World Government appearing every 20 years that wears a straw hat.
This reappearance of people wearing straw hats throughout history who challenges the World Government could be why Im is comparing the straw hat in his vault with Luffy’s bounty poster. It is pretty likely that Im is in fact comparing the straw hat in the chamber which could be from the Void Century with the straw hat Luffy has on his bounty poster.
If there is a pattern of new enemies of the World Government wearing straw hats every 20 years or so which all goes back to the Void Century, then why do the World Government just not ban wearing straw hats and focus killing any new rookie pirate wearing a straw hat? Would that not prevent that there was a straw hat for every new generation?
Maybe they have already tried that, and the result is that a new protagonist with a straw hat emerges regardless. Perhaps banning straw hats would raise questions about the reasoning behind the ban and perhaps the history of the Void Century.
I think that Im is scheming to end the cycle of people with straw hats representing the Will of D who challenges the World Government.
We know that when a devil fruit user dies, the devil fruit reappears in the One Piece World. There might be a connection to how devil fruit powers reappear and how people with the will of D wearing straw hats reappears throughout history.
If Im wants to break the cycle of new straw hats emerging every 20 years challenging the World Government and the reapparance is related to how devil fruits reappear, then would it not be natural for the World Government to assign Vegapunk to research this?
We know that Vegapunk is researching devil fruits based on his work with replicating the powers of Kizaru to Pacifista, his connection to Caesar who makes SMILEs etc.
Perhaps the answer to how devil fruits are able to reappear lies in the lineage factor that Vegapunk researched with Judge.
Maybe when one eats a devil fruit, they obtain a lineage factor responsible for the power granted by the devil fruit.
The Pacifista may be product of Vegapunk manipulating the lineage factor for Kizaru’s devil fruit ability into the cyborgs.
What if the same is possible for the will of D, that the current straw hat has a lineage factor representing the Will of D that can be inherited through death similiar to devil fruits?
This lineage factor would then be responsible for the reapperence of straw hats after their death, thus repeating an endless cycle of straw hats with the Will of D throughout history.
This could certainly explain why Im compares the bounty poster of Luffy with the straw hat in the chamber in Mary Geoise. Try to imagine Im taking stock of Luffy and grumbling over why new people wearing a straw hat representing the Will of D keeps appearing repeatedly throughout history despite his efforts.
We know that Judge was able to manipulate the lineage factor of his children causing them to become fierce warriors that obeyed Judge, except Sanji of course. It could be that the goal of Vegapunk’s research is to somehow manipulate the lineage factor of the current straw hat in a way that breaks the cycle of reemerging straw hats. 26 years ago, Roger got an incurable disease.
Imagine Im around 26 years ago in Mary Geoise throwing a dagger at a picture of Roger just like we saw in chapter 908 and Im force Vegapunk to make something to take care of Roger.
What if the strange uncurable disease that Roger got was a product of Vegapunk’s research that was supposed to end the cycle of reemerging straw hats throughout history?
Perhaps Vegapunk build some sort of chemical weapon like a virus that could destroy the lineage factor that allowed other people to inherit the “Will of D” and reemerge as the new straw hat.
*Theory by MammothBoy78
