Among all the long-term manga serials out there, only a handful come close to One Piece in its expert use of foreshadowing. Creator Eiichiro Oda will hint not only at future events to come but also future characters and sweeping changes that can greatly affect the world he's created.
One Piece has countless moments of foreshadowing, some very well known to fans. But here are five of the more overlooked hints that have also had excellent payoffs throughout the series.
Races in One Piece
The first major incident during the Sabaody Archipelago arc comes when the Straw Hat Pirates' newest friend, Camie the Mermaid, is kidnapped by human traffickers. One of Sabaody's less welcoming attractions is its Auction House where nobles and royalty can come to purchase slaves -- and Camie's about to become one of those slaves. In Chapter 501, as the Straw Hats and The Flying Fish Riders scramble across the Archipelago to find Camie, Duval shows Sanji the price list that each race typically goes for in the Auction House.
It's truly disgusting, but what's noteworthy is how the list mentions several races readers hadn't yet met in One Piece, such as Dwarves and Minks. We don't properly meet the Dwarves until Dressrosa when Robin and Usopp befriend the Tontatta Tribe. The first Mink introduced is Bepo the Bear during the Sabaody arc, but he's only revealed as a Mink during the Zou arc.
CP-0's First True Appearance
One interesting revelation to come out of One Piece's time skip was the existence of CP-0, the strongest Cipher Pol organization. While the other nine branches are given directives from the government, CP-0 takes direct orders from the World Nobles. In Dressrosa, three unnamed and masked operatives reveal to the citizens that the newspaper printing Doflamingo's resignation from the Shibukai was a lie -- but this might not have been CP-0's first appearance.
In Chapter 595 -- right before the time skip -- there's a conversation between Doflamingo and a shadowy figure wearing a bowler hat. The man bears a striking resemblance to the same CP-0 agent who wore a white suit and bowler hat in Dressrosa. It's a small detail that's easy to miss, but it subtly hints at Doflamingo being a former World Noble.
Gekko Moriah Namedrops Kaido
Considering how big of an antagonist Kaido currently is in the One Piece manga, it's hard to believe that back before the time skip, we knew next to nothing about him and Big Mom. The Yonkos' names after Water 7 were only revealed when Koby speaks to Luffy about the New World, but there's a bit more about Kaido in the Thriller Bark story arc.
When we first meet Gekko Moria, he's a selfish and lazy captain who overly relies on his crew to get what's needed. This is because Moria previously clashed with Kaido, with the resulting battle killing off Moria's entire crew. He blamed the defeat on his crew's lack of strength, explaining how he'd become overly reliant on his new zombie army. This battle also established early on just how powerful Kaido actually is. Seeing Kaido in action now, it makes complete sense that he defeated Moria and wiped out his men.
The Land of Wano, First Mentioned by Dr. Hogback
Eiichiro Oda loves teasing his audience with bite-sized information that later snowballs into vital plot points further down the line. Another example is the first mention of Wano Country, where the current One Piece arc is taking place.
When the Straw Hats arrive at Thriller Bark, Usopp, Nami, and Chopper get separated from the crew and are confronted by the deranged Dr. Hogback. Hogback introduces the cowardly trio to one of his strongest zombies, Ryuma, saying the samurai harkens from the land of Wano. In the end, Zoro went toe-to-toe with Ryuma and claimed the samurai's legendary blade, Shusui.
One Piece's First Mention of SMILEs
After The Straw Hats and Silvers Rayleigh attack the Auction House in Sabaody Archipelago, the owner, Disco, uses a transponder snail to call Doflamingo for help in One Piece Chapter 504. It turns out the twisted warlord runs the slave trade, but then gives it all to Disco, saying "Slave trading is getting old, idiot! This is the era of the SMILE."
It's later revealed that Doflamingo was referring to his artificial devil fruit, manufacturing through Caesar Clown to sell to Kaido. SMILEs have had an ongoing effect from Punk Hazard to Dressrosa, all the way to Wano. Seeing how it's used and the effect it has on people, it only makes sense that Doflamingo would be involved in such an unethical practice.