What is One Piece? The critically acclaimed and best-selling manga has been exploring this idea since the series' inception when it opened its gate to the vivid and romantic speech of Gol D. Roger. "My treasure? If you want it, I'll let you have it. Go look for it. I left all of it...at that place."

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Since those famous last words, the One Piece world has been ravaged by pirates on the hunt for the overzealous treasure; an for more than 20 years, none has found it. Throughout the years, there has been a lot of speculation as to what the One Piece is and how it connects to the series' greater story if at all. This list will be looking at some of the fan's own ideas as it looks at some of the most well-thought-out fan theories (& a few that are just ridiculous).

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10 Thought-Out: It's The Ancient Weapons

Since the Alabasta Arc, the series has teased that there are three Ancient Weapons hidden within the world. Crocodile was searching for the great battleship, Pluton, the blueprints for which were in the possession of Franky's master, Tom. Poseidon turned out to be the Ryugu Kingdom's Princess Shirahoshi who was prophesized to one day command all of the world's Sea Kings.

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The whereabouts and identity of Uranus are still unknown. Given their level of importance within the series' history and the World Government's own paranoia as to who may find it, there's reason to believe that the One Piece itself could be Pluton, Uranus, or some hidden amalgamation for all of them.

9 Ridiculous: It's Luffy's Straw Hat

Imaginations first started going off when the story revealed that the Straw Hat had once belonged to Gol D. Roger, possibly insinuating that it itself was his greatest treasure or, at least, had some connection to it before giving it to Shanks.

This would only see more uproar when the series revealed a giant, preserved Straw Hat within Im's vault. Fans have started to think that the Straw Hat itself could be the treasure, that it could be some sort of ancient crown, or that it even hides some great secret within its red band.

8 Thought-Out: It's The Origin Of The Devil Fruits

Despite being heavily used throughout the story, the Devil Fruits are still one of the biggest mysteries in the series. They've been speculated to have some connection to the Devil; and because of that, Devil Fruit users can't swim, because they've been cursed by the gods of the sea.

Scientists in the One Piece world have tried to debunk such legends but haven't had much luck in discovering their secrets, though they have found a way to engineer some bargain bin ones. Given the fruits' importance and mystery in the world, some fans are thinking that the One Piece is the very origin of all Devil Fruits, perhaps even a great tree that's growing them.

7 Ridiculous: It Is A Devil Fruit

Following along the Devil Fruit route, some fans have started to believe that the One Piece itself is a Devil Fruit but a very special one. The world is rife with various mysteries and, as a way of compartmentalizing all of their answers to one origin, the One Piece has been thought to be the origin of all of them.

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It could be the most powerful Devil Fruit of them all that people fought over and feared centuries ago. It could have the power to erase people's memories, creating the Void Century. It could tie into the Voice of all Things. It's a hodgepodge of the various mysteries surrounding the One Piece world that, while interesting, doesn't give Eiichiro Oda enough credit for his planning.

6 Thought-Out: It's Another Poneglyph

When Roger first landed on Laugh Tale, all he and his crew did was gaze at something. Not too long after, Roger began to laugh with a great smile on his face, dubbing the island Laugh Tale because of this experience. This has made fans wonder what the One Piece could possibly be if it was able to just make Roger laugh upon just seeing it.

One idea being that Roger was reading something and that the One Piece is another Poneglyph that left behind a crucial message. It could be Joy Boy's last words or even the entirety of the world's true history. Either could justify the World Government being worried over it, and such truth left on well-documented writing could cause the massive stir that'll have everyone fighting to reshape the world.

5 Ridiculous: It's Friendship

This one's ridiculous mostly due to the fact that it would spit on the face of over 20 years worth of build-up. While the creator himself has said that the One Piece will actually be a thing and not something vague like friendship, fans still speculate that it's tied to friendship in some way and that the One Piece will have the Straw Hats leaving Laugh Tale with nothing more than a cheesy lesson.

It's a theory that plays on the anti-climactic tropes that have plagued detailed mysteries in fiction, and the series' ongoing themes of friendship.

4 Thought-Out: It's The Ancient Kingdom

One of the biggest theories tying the One Piece to some of the series' greater lore is the idea that it is the Ancient Kingdom itself. During the Void Century, the kingdoms that would one day band together to form the World Government overthrew a prosperous and highly advanced kingdom.

In this case, the One Piece could not only be the reveal of the Ancient Kingdom but could be the entire kingdom itself. It could be a dilapidated city or even a fully preserved yet hidden civilization (possibly the "D" clan).

3 Ridiculous: It's The Ancient Kingdom...On The Moon

The scholars of Ohara sacrificing their lives before the Marines' Buster Call hits during One Piece's Enies Lobby Arc

This is a pretty hefty one that got major attention after it was featured on the One Piece Podcast website. The idea is that the Ancient Kingdom and, perhaps, the One Piece itself is on or from the moon. When Eneru traveled to the moon, he found a hidden community of androids that were being threatened by Space Pirates.

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While there, he found various ancient texts whose symbols seemed to resemble the Skypeian people. This has left many to believe that the Skypeians were once from the moon or have at least traveled there and are actually an angelic race. With that in mind, Laugh Tale could be where some of those ancient people once lived or could be hiding some mechanism that can bring people to the moon.

2 Thought-Out: It's The Destruction Of The Red Line

Bringing world peace, the Ancient Weapons, and the All Blue under one neat packaging, some fans think that the One Piece could very well be a unified world. Using the Ancient Weapons, one could destroy the section of the Red Line funnels between every sea and the Grand Line.

Doing so would connect every sea into the "All Blue" and the entire world into "One Piece." This would create unity if not at least better travel between kingdoms, but it also means the destruction of the Celestial Dragon's Holy Land, Mariejois which may be why the World Government is so worried about people discovering the idea.

1 Ridiculous: It's Just A Prank, Bro!

This has always been a popular idea between memes. Once Luffy or whoever gets their first comes across the One Piece, they'll find a note explaining that it was all a hoax or that the One Piece is just the first piece of many, making the entire adventure just a wild goose chase.

However, after the series first revealed Roger's reaction to Laugh Tale, people are speculating even more that the One Piece itself could just be a big joke. This would tie into Joy Boy's moniker, and some people have even begun thinking that Joy Boy himself was some sort of ancient trickster. In any case, a lot of fans won't be laughing if this is true.

NEXT: One Piece: 5 Heroes That Are Underused (& 5 We See Too Much Of)