Depending on how imaginative and fun-loving a creator is, they may slide certain Easter eggs into their art as either nods to other creations, hints at the future of their series, or just as fun little things for fans to find.
One Piece is one of the longer manga and anime to date and the creator Eiichiro Oda loves tossing in little Easter eggs for people to find. He's a master of world-building, and many of the little tidbits he sprinkles into One Piece are very easy to miss if you aren't paying close attention.
10 Pandaman — He can be found in the anime & the manga usually in the background with other characters
Pandaman is one of the more fun Easter eggs to try to find throughout One Piece. He can be found in the anime and the manga usually in the background with other characters. His body type also tends to change as well, so the only consistency is the panda head he has.
He's rarely up front and personal in either the anime or manga, so try scanning background characters to see if you can catch Pandaman. There are some other characters you can find as well like pandawoman, but so far pandaman is the most common that you'll find.
9 Lola's Vivre Card — Nami only knew that it was Lola's mom's card, not that it belonged to the Emperor Big Mom
Oda is well known for his world-building and littering the series with clues and hints to upcoming events. One of these was back at the end of the Thriller Bark arc when Lola gave Nami a vivre card that could potentially help later. Nami only knew that it was Lola's mom's card, not that it belonged to the Emperor Big Mom.
It was completely forgotten about until later on in the Whole Cake Island arc. Big Mom's homies were afraid of the vivre card because it contained part of her soul and Nami used that to her full advantage while on the island. Oda planned her use of it well in advance and only fans that kept track of the vivre card weren't surprised when it became useful.
8 Usopp's Fables — Most of Usopp's fables actually became true later in the series
Particularly before the time skip, Usopp was known for embellishing on the truth. He had so many lies he told as stories that they became known as Usopp's fables. Most fans began dismissing these stories as utterly false, but Oda wrote each of these lies cleverly.
Most of Usopp's fables actually became true later in the series. Among these lies that became truths were that pirates were attacking (they did), there was a giant goldfish that pooped as large as islands (brogy and dorry's island), and that he has 8,000 followers (when he became God Usopp in Dressrosa).
7 Oda In The Anime — so far, the books are the only known self-insert Oda has done
One of the most common Easter eggs in any series is the creator putting themselves into the world. Some tend to put themselves as an obvious character, but Eiichiro Oda is a bit more subtle than that. On a rare occasion, he showed a series of books with one of them showing the title One Piece and the other had his name on the spine.
This is one of the few occasions that Oda has put himself into the series, but there are likely several other instances of this happening. Some people try to scour through the manga for instances like these, but so far the books are the only known self-insert Oda has done.
6 Luffy Drew Franky — It's like Luffy knew exactly who his shipwright would be before they even met
The Straw Hats were sailing into Water 7 knowing that they needed to add a shipwright to the crew. While the crew discussed how they were going to find someone, Luffy decided to draw his ideal shipwright. Oddly enough, his drawing is pretty much exactly who they ended up finding.
It's not a perfect match, but that drawing is basically Franky. It has Franky's signature shades, the large forearms, the general blue color, the robotic nose, and neither of them have pants. It's like Luffy knew exactly who his shipwright would be before they even met.
5 Luffy's X Scar — Oda hinted that Luffy would get an injury like this far before Marineford
Luffy's X-shaped scar on his chest came during the Marineford arc when Akainu gravely injured both Luffy and Jimbei. This X has been on his chest ever since the time skip and is clearly here to stay for the rest of the series. However, Oda hinted that Luffy would get an injury like this far before Marineford.
Back in episode 223 of the anime, Zoro ended up attacking Luffy against his will. Luffy got slashed by Zoro across the chest in an X shape. This injury healed, but it wasn't long before Luffy got a permanent scar in the exact same shape. This was a clue that very few people realized until later.
4 Crossover — The biggest nod to Naruto has to be the cover of the manga for chapter 766
It was no real secret that Oda and the creator of Naruto highly respect each other. As a way of showing this, both artists were prone to tossing in little nods to each other in their own respective pieces. The biggest nod has to be the cover of the manga for chapter 766.
This art is full of nods to Naruto. Naruto himself is eating behind Nami while Luffy is eating the famous Ichiraku Ramen. Nami's dress is also covered in the symbol for Konoha, with a minature fox to represent Kurama beside her.
3 Sanji's Royal Blood — The only clue that Oda gave to readers & viewers was Sanji's strange choice of nickname
Sanji's backstory hadn't been fully revealed by the time the Alabasta arc rolled around. It was revealed later that he was in fact a prince of the kingdom of Germa over two years later in the series. The only clue that Oda gave to readers and viewers was Sanji's strange choice of nickname.
Sanji had to contact the higher ups of Baroque Works, who used nicknames based off of a number or word following Mr. or Mrs. Sanji decided to use the name Mr. Prince, which didn't make much sense until you realize some time later why he chose that name.
2 Laboon — During the Thriller Bark arc, the Straw Hats ran into a skeleton named Brook who was the last pirate from an old crew
Laboon was a shockingly large whale that greeted the Straw Hats as they first entered the Grand Line. He was in a state of depression because he was abandoned by a pirate group long ago. There wasn't much detail given about the pirates that abandoned him, but it was clearly an important bit of information that Oda wanted the viewers to know.
During the Thriller Bark arc, the Straw Hats ran into a skeleton named Brook who was the last pirate from an old crew. It was revealed that he wanted to get back to a dear friend who his crew had to abandon years ago. That friend is, of course, Laboon. Oda put that little hint into people's heads long before they met Brook.
1 Robin On The Going Merry — Her being on the ship & so relaxed was a tip that she would join the Straw Hats later on
For the most part, enemies have never been shown on the Straw Hat's ship. Both the Going Merry and the 1000 Sunny are safe spaces for the Straw Hats, but more so the Going Merry. The Sunny had to deal with Big Mom and some minions of Caesar Clown, but Merry only had a single enemy set foot on it.
Nico Robin showed up on the Merry before the Straw Hats even set foot on Alabasta. She appeared completely comfortable on a ship surrounded by enemies, and Oda absolutely intended this as a tip for the future. Her being on the ship and so relaxed was a tip that she would join the Straw Hats later on.