Theory The National Treasure of Mary Geoise is Joyboy's brain

[Fox666]

This theory ties in with the theory that the Gorosei are Imu's satellites

When the National Treasure of Mary Geoise is "revealed", we see Imu looking at a giant hat. The room is kept at freezing temperature, and Doflamingo said the power of the treasure "rots" away. That tells me the treasure should be organic matter.

The hat is not actually the treasure in itself, the treasure is actually the top of Joyboy's head that was sliced off, along with the hat. The real treasure is the brain under the hat. Joyboy has never been stated to be dead, because technically he isn't dead.

There are only 5 Gorosei because Imu was also one of Joyboy satellites, who betrayed Joyboy similar to what York did to Vegapunk. 1 and 6 in Japanese can be read as "i" and "mu", and Imu actually means "1 out of 6".

There are tubes in the freezing room, meaning it was some sort of facility or laboratory. Vegapunk mentioned the satellites synchronize once per day, and this area must have been Joyboy's synchronization chamber.

That's why there 7 holes in the wall, and one of them has the hat inside. While not visible, there should be tubes coming from below that connects to the brain.

 

[Bradhimself]

I like the aspects of why the room is cold, and the quote from Doflamingo about it rotting away. I just doubt anything so gruesome would be in this story tbh.

I also doubt JoyBoy still being alive as his fruit has moved on, which happens after death.

The satelite thing might be a real possibility, but I personally dislike that idea, since it has just been done with Vegapunk.

 

[Hannibal Psyche]

This makes no sense.
Doflamingo wouldn't look at a brain and think "wow this must be the biggest secret in all of Mariejoa".

The National Treasure is most likely Imu and the reason why knowledge of him will shake the world like Joker said is because the world think there isn't 1 leader who rules the world, but a democratic rule.
A brain is not going to be significant news to the world, all they'd have to say is it is for science and it's the brain of some ancient speices... what's most likely the case is Joker saw Imu on the throne where the Swords are, and keeping that a secret is why he was allowed to be a Shichibukai.
A brain is simply not going to result in that.

Plus Joker said Law's powers would allow him to use the National Treasure which would likely be personality transplant. If he took over Imu's body, he would literally rule the world.

I don't think Law's powers have any purpose with a brain that's just there.

 

[Vanshrimp]

if i had to pick a vital organ, i would have gone for the heart which seems to be still beating, (and these beats can bring zunesha, giant robots, the mystery creatures from thriller bark, creatures from the skies, and who knows what lurking around) that is why it has to be kept in a cold room, and perhaps, it has to be in that state because if stops, a world wide sinister occurs, (sun could explode or something)

 

[RaisinRisin]

Interesting theory. During the fight scene in Dressrosa with Law I'll point out though, Doffy didn't say the treasure was rotting away. He just said he knew about a giant treasure in the holy land of Mary Geoise. I'll have to look at that scene with the giant hat again to see if I can find those tubes. Maybe there's a hint there on whether they're for refrigeration purposes or otherwise as you've suggested.