It starts with the statement that our man Doflamingo made this chapter 906
Notice that Doffy calls it the secret treasure that is hidden, not that the treasure itself originally belonged to the Tenryubito. This is very important to prove a point that it makes no sense for the Celestial Dragons to have anything that they themselves value as a treasure since they can technically own everything they desire, which would explain (in part) their spoiled nature and behavior.
I also think that the power Doffy is referring to in this panel is the Tenryubito’s power/status that they presently have. Doffy even said “The Celestial Dragons will be dragged down their high horses” in the “Throne War” speech, it lines up pretty well with the “power degrades quickly” statement here.
Basically their power is degrading, the world is more chaotic, pirates are balooning, they are essentially losing control little by little.
Remember that Law said “D. will bring forward another storm”
And one that is carrying this storm of disorder forward is our boy Luffy, who manages to have something that can symbolize it, his hat.
Which leads down to the straw hat that we saw at the end of chapter 906.
I don’t believe that the straw hat itself has any magical powers, and I don’t believe that it is the thing that Doffy said to Law that would give him reign over the world if he had the Ope Ope no Mi devil fruit. Oda showing us the hat here doesn’t mean that there is a direct correlation to whatever treasure Doffy mentioned to Law (and its power), but rather an indirect one. I think that will be revealed later down the story.
Also, notice the hat is perfectly fit for a Giant. So, I think that the hat represents something else:
There are 6 spots in the vault that are empty.
And these are the D. family names that we know of thus far:
- Monkey D.
- Trafalgar D.
- Gol D.
- Marshal D.
- Portgas D.
- Jaguar D.
- ???????
Did the strawhat that we saw in chapter 906 belong to someone that previously carried on the Jaguar D. family’s will ? If so, this means that by keeping the hat in the vault, the Tenryubito practically shut down the process of passing down the will, and the ideology that it represents, of this particular lineage.
We can extrapolate this process for all the remaining hats and it’s possible that the Tenryubito would shut down the idea of freedom that the hats represent, virtually forever, achieving their ultimate victory.
CONCLUSION:
The vault’s purpose is to keep the straw hats as trophies(and has reminders) for cutting off a particular lineage of inherited will that, if left unchecked throughout the ages, will bring ruin to the Celestial Dragon’s rule by replacing their ideology for the thing that the strawhat represents: Freedom.
This is why this particular shadowy figure is bringing the bounty posters as a comparison check and to possibly acknowledge the threat that Luffy represents.
Will this finally be the trigger that will make the Tenryubito treat Luffy as a serious problem to their foundation, and thus bring a whole new level of danger to Luffy and the crew?
*Theory by Keisoku