WARNING: The following contains spoilers for One Piece Chapter 1044, "Warrior of Liberation," by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English from Viz Media.
One Piece fans have theorized about Joy Boy and his connection to Luffy for years now. Arguably, the most popular theory was that Luffy is Joy Boy reincarnated. It's a controversial theory among fans as many hate the idea of Luffy's character falling under the Chosen One or Child of Prophecy tropes like many other protagonists do. Fortunately for everyone, this is not the case.
Luffy does have a connection to Joy Boy, but not in the way most fans have speculated. It seems his connection to Joy Boy is through his Devil Fruit. Luffy's Devil Fruit, the Gum-Gum fruit, is not exactly what it was believed to be up until now. In Chapter 1044, the Five Elders revealed that Luffy's Devil Fruit was actually the Human-Human fruit and it's not a Paramecia type. It's a mythical Zoan fruit and the model is 'Nika.'
Nika seems to have been a mythical warrior from ancient times who was venerated as the Sun God by slaves who believed he would liberate them. Nika was first mentioned by Who's-Who in Chapter 1018. He heard about the legend from a prison guard who suddenly vanished after telling the tale. He took this to mean that the information was likely meant to be kept a secret and the World Government didn't want it getting out. Chapter 1044 proved that his thoughts were correct and there's much more to it.
Nika's legend is clearly reminiscent of Luffy's character arc. From the very beginning of One Piece, Luffy has been liberating people from all kinds of suffering. Each member of the Straw Hats was freed from an undesired situation by Luffy whether it was a villain's tyranny, loneliness, imprisonment, impending unjustified execution, etc. Luffy has never been one to stand by and let others suffer. He has liberated entire nations from oppression for no greater purpose other than it simply felt right to him.
The World Government has apparently been desperately trying to acquire the Human-Human fruit for over 800 years. They claim it was so elusive that it's almost as if the fruit itself was evading them. Initially, this seemed like a joke. However, they go on to casually mention that all Zoan fruits have a will of their own and this one carries the name of a God. It's unclear what exactly they mean by this, but if it's what it sounds like, then it makes sense why Zunesha said Joy Boy has returned in the previous chapter. After all, it can't be a coincidence that Luffy awakened the Human-Human fruit and gained his new Gear 5 form just as Joy Boy has supposedly returned.
The Human-Human fruit grants its user's body the properties of rubber. It's said that they're only limited by their imagination and are the embodiment of the Warrior of Liberation (Nika), putting smiles on faces far and wide. Awakening the fruit greatly increases the strength of their rubber body, giving them more freedom. The Five Elders claimed it's the most ridiculous power in the world. All these details are why the World Government is adamantly trying to eliminate Luffy. There's still plenty of mystery surrounding the Joy Boy situation, the Human-Human fruit, and Zoan fruits in general. Luckily for fans, it seems the time for the mystery to completely unravel, is now.
