Fans of One Piece believe that the biggest mystery in the series concerns the nature of the treasure that gives the best-selling manga of all time its name. However, another mystery, still concerning the One Piece, will likely never be solved and hides behind an incredibly sad story.
One Piece is the name of the greatest treasure in the world, left behind by Gol D. Roger, the only man in history to achieve the status of Pirate King. The One Piece waits on Laugh Tale, an island hidden somewhere on the Grand Line, the most dangerous sea in the world. The nature of the One Piece is a mystery, but just the mention of its existence, made by Roger moments before being executed, was enough to usher in a new Pirate Age, unleashing hordes of adventurers and scoundrels who took to the seas to find this legendary treasure. Eiichiro Oda, the author of the manga, said that he knows exactly what the One Piece is, but he will only reveal it at the end of the story.
Oda shared this secret with very few people in the world, including his editor, who was told as a birthday present. He also debunked one of the main theories regarding the One Piece, that it would not be a treasure at all. However, a story that has been circulating since 2014 says that Oda actually shared the secret with a child dying from cancer, who asked to know the nature of the One Piece as part of a Make-a-Wish-style initiative. Apparently, Oda gladly complied, and after that, the kid was seen smiling and crying, and said "One Piece is beautiful". This would be an incredibly touching story if it weren't for the fact that it's most likely fake.
The news was originally shared by the website kdramastars.com. After that, it was picked up by a good number of websites, but the only source they ever cite is the original article from kdramastars, which mentions a source called JapNation AniManga that does not exist. No reputable news source or One Piece-related outlet has ever reported about Oda doing a Make-a-Wish, so the most likely explanation is that the story was entirely made up. However, there has also never been any official statement or denial, the original article is still online, and the story keeps resurfacing periodically. The only argument is that the source of the news is questionable and that no other media outlets picked up the story.
The story of Eiichiro Oda revealing the secret of the One Piece to a child dying of cancer is most likely fake, but it also took on a life of its own to become a little mystery inside the mystery. While it's disgusting that someone could speculate on childhood cancer, there is still a tiny chance that Oda did share the secret in similar circumstances. After all, One Piece has been going on for 25 years, and even if it's really sad to think about it, there will be people who will never get to see how this amazing story ends.
Source: One Piece Reddit