Popular theory explains what the One Piece treasure is.

SUMMARY

The One Piece Treasure, which would bring Eiichiro Oda’s masterpiece to a close, is still a mystery nearly thirty years later.

However, a theory concerning the One Piece treasure makes the most sense and provides a reasonable explanation for the treasure’s components.
The theory states that Luffy’s ridiculous Gear 5 form may have disclosed the One Piece Treasure’s actual nature.

Even after almost 30 years, the One Piece Treasure, which would conclude Eiichiro Oda’s magnum opus, still remains a mystery. One Piece fans and the Straw Hat Pirates have been searching for the treasure for so long that they have developed multiple theories about what the contents of the treasure could be.
One Piece has entered it's final arcOne Piece | Toei Animation
Some believe that it is one of the Ancient Weapons that will be used to destroy the evil of the World Government, while others believe it is a sake that will bring the world together. However, there is one theory about the One Piece treasure that makes the most sense and has a credible explanation of the contents of the One Piece treasure.

According to the theory, Luffy’s absurd Gear 5 form might have revealed the true nature of the One Piece Treasure, which is essentially a comic book that motivated Joy Boy to rebel against the World Government and try to save the world from their tyranny.

Theory Claims One Piece Treasure is a Comic Book

According to u/RoronoaLuffyZoro on Reddit, there are multiple pieces of evidence that prove that the One Piece Treasure is actually a comic book. The theory states that as Nika is a mythological character in the One Piece world, he could be the main character of this comic book that was Joy Boy’s treasure.

This comic book helped him stay positive and happy during the dark times of slavery, just like the legend of Nika helped other slaves. The comic book helped him desire freedom for himself and others, and this desire was embodied in a Devil Fruit that gave him the power of stretching and hence came to be known as Hito Hito no Mi, Model: Nika.
Gol D. Roger Talking about One Piece | Viz MediaGol D. Roger Talking about One Piece | Viz Media
The fact that Roger called the treasure a “tale full of laughs” is another clue that supports the theory of the One Piece treasure being a comic book, as comic books are generally fictional stories that make people laugh. Although each of these proofs offers a fresh angle on the One Piece Treasure’s status as a comic book, Luffy’s Devil Fruit stands out the most.

Luffy’s Gear 5 Sheds Light on the One Piece Treasure

Although there is enough evidence to prove that The One Piece Treasure is a comic book, Luffy’s Gear 5 is the most important one. According to the One Piece narrative, it has already been established that the previous user of Luffy’s Devil Fruit was Joy Boy.
Vegapunk Explains Joy Boy's Powers | Viz MediaVegapunk Explains Joy Boy’s Powers | Viz Media
Therefore, Joy Boy is the one who manifested the Devil Fruit with his strong desire for freedom. He most likely desired the power of Nika (stretching) and combined it with the comic book (his treasure), and the resulting power became his biggest weapon in the battle against the World Government.

As the power was from a comic book, it looked cartoonish and comedic. Even Kaido claimed that the newfound power of Luffy looks like something out of a comic strip. Therefore, it can be pointed out that Joy Boy’s greatest treasure that motivated him to stand against the tyranny of the World Government was a comic book.