Okay guys,you all saw the name of the writer under the title of the theory,so you knew what you were getting into,though I still apologize in advance.You know the drill,you sit tight,enjoy the ride,and read everything so that you can complain to me later about how long the theory was.I'll try to make this worth your while.Also,some of the things I'm about to mention,are very similar with a couple of things said in the theories written by @Finmordil and @thisisbignews .I'd like to mention them since,as you'll find out,I've had the same ideas as them (up to a point) and their theories are worth reading in my opinion.Now then,let's get to it. Let's start from the AK,the kingdom ruled by a clan that had the secret name of "D" in their names.We already presume that much,but did everyone that lived at the AK have the name of "D". Considering the size of the kingdom,and the survivors that hold the name of "D" right now,I wouldn't say so myself.So it would have been highly possible for there to have been people with substantial power and information in it without the name of "D" that wanted to overthrow the rulers at the time.Were those people the celestial dragons? I don't think so,they were the Gorosei,who persuaded 20 (at least) kings to help them with overthrowing the AK in exchange for the rank of world royalty,the rank that's now known as Celestial Dragon.The main reason as to why I came to that conclusion,and it's the same reason why I assume it wasn't just the Gorosei that betrayed the AK,is the black figure on Ch. 906. Spoiler: Black Figure The way that figure goes to look at the hat right after Luffy's bounty skyrocketed,shows that it had a connection to the original owner of the straw hat.Now then,here's two questions: 1. How are the Gorosei still alive? 2. Who was the original owner of the hat? Keep those questions in mind as we change gears and progress further. Gol D. Roger,the pirate King.Here's a question for you.Why is he being regarded as the Pirate King and by who was he regarded such at first? Yup,because he found the One Piece.But the question is,where did he find it.Recall Roger's words before his execution,the words that were in the opening sequence of the very first episodes. Spoiler: Roger's Words You want my treasure? You can have it! I left everything I gathered together in one place.Now you'll just have to find it! "...I left everything..." From those words we know that now the One Piece is at Raftel,but: 3. Where was it before Roger left it there? 4. And in the end,who labelled Roger "Pirate King" at first? Keep these two questions in mind and let's proceed even further. The national treasure hidden in the holy land of Mary Geoise.I partly agree with the recent theories about it,that it's a collection of corpses of people from the AK.But what about the hat? I believe that the national treasure is not just a collection of corpses,but also objects with the conscience/soul of some people from the AK (or connected to AK) in them.And not corpses of jut normal people that lived in the AK,but corpses of D's.By the way,kudos to @Storm chaser for noticing that there are "many" crypts in that underground place.The light in the crypt with the hat probably made many people in general miss that at first (perhaps). Here's a couple of questions though? 5. Why did the WG not simply kill off the D's and instead preserved their bodies and objects with their souls? It's not like it's not possible,Saulo died,Rouge died,Ace died,Roger presumably died. Spoiler: Roger's last words to Reyleigh 6. In the end,what is the One Piece? It's okay,don't worry,you don't have to keep this one in mind.Now that we're established some presumed (by me) facts and known facts and pondered some questions,let's get to the answering part of the theory. I believe the One Piece to be a device/artifact/object that possesses the ability to impart one piece of the person's soul into an object or body of their choosing of their choosing.The OP was originally located at the AK where the kings used it to impart part of their souls in a certain object before passing it on to the next and passing away.If anyone has ever read "Noblesse",recall the soul weapons.The kings of the AK didn't misuse the OP by imparting a piece of their soul into a new body,but there were some who were attracted by the idea of immortality,namely the Gorosei.Fueled by their desire to live forever,they decided to destroy the AK and steal the OP.The reason why the preserved the corpses of the D's and the objects with their souls,is because the OP presumably works only by reacting to the souls/objects of the D's.So they kept a body/object for each person who wanted to stay immortal.The black figure we saw in Ch. 906 could be the person behind even the Gorosei themselves who was connected to the first owner of the straw hat,and uses it to gain immortality.And that original owner,would be Joy Boy.Joy Boy,despite failing to keep his promise,was very certain that someone else would fulfill it in his stead.Why would he think like that...unless he had imparted his soul into an object that would hold on to that promise and impart it on someone else (the size of Noah could also be a small hint to Joy Boy's size,that would correspond to the size of the straw hat at Mary Geoise,but not so much really). But the hat is at Mery Geoise,so this begs the question of how that promise has been passed on.The answer to that is the same as to why the Gorosei are no longer immortal and have started to age.After centuries of living,there came a man who stole the OP from the WG,preventing them from imparting part of their soul to new bodies while they continued to age more and more.That man was a survivor of the "D" bloodline and the very first pirate king,Gol D. Roger.When he stole the OP from Mary Geoise,Roger could hear the voice of Joy Boy soul with his ability to hear the voice of all things.After he stole the OP,the WG branded him as the first pirate king (it was like giving him the highest bounty) in order to prompt people to capture him and consequently bring the OP back to them.But Roger didn't let them,he hid the One Piece in the best possible location,Raftel.But.before he died,he used OP to impart a piece of his own soul to his straw hat.He then entrusted that hat to Shanks. Wait,wait,wait though.Does that mean that Shanks is a "D" or that he has the ability to hear the voice of all things? No,I don't think so.Think about it,does Shanks seem like he wants to become the pirate king? Not to me.He's the only one of the Yonko who doesn't have that particular ambition.The reason for that is because he already knows everything from Roger,and he was entrusted the hat simply to give to the right person.Think about it,why did Shanks give the hat to Luffy? Sure,his personality is similar to Roger's,but is that all there is to it,to go as far as sacrificing an arm? Maybe he knew Luffy was both a "D" and that he had the ability to hear the voice of all things.Think about WB's words to Teach,that he wasn't the man Roger was waiting for.I believe that as Luffy's ability to hear the voice of all things gets better and better,he'll eventually be able to hear the voice of the object he's had on him since he was young,his straw hat,which holds Roger's soul,which in turn holds Joy Boy's promise as well. This is end,I hope you guys enjoyed it despite the long text.This was a theory made by Yuuzume.