Since debuting in 1997, One Piece has become one of the most recognizable media franchises in the world. The series is the best-selling manga of all time, and as indicated by the massive wave of hype surrounding the release of its live-action adaptation, Monkey D. Luffy and his crew show no signs of slowing down.
As the Straw Hat Pirates travel across the Grand Line, they encounter a wide variety of individuals, many of whom are just as interesting as the series' protagonists. Since One Piece's narrative is almost always focused on Luffy's adventures, these supporting characters rarely receive their time to shine — an issue that could easily be addressed if they were subject of their own spin-off series.
10 Mont Blanc Noland
400 years before the events of One Piece, a storied adventurer named Mont Blanc Noland roamed the Grand Line. Noland's travels happened long before the Golden Age of Pirates, but even without the allure of finding the One Piece, he prided himself on exploring the seas, eventually leading him to a variety of iconic locations.
One Piece provides little information about events that transpire before the life of Gol D. Roger; therefore, a spin-off series documenting the adventures of Mont Blanc Noland would be a great way to investigate the histories of locations like Jaya and Tontatta Kingdom. Noland garnered an undeserved reputation as a liar following his death, so a series centered around his life would go a long way in clearing his name.
9 Portgas D. Ace
Out of all the deaths in One Piece, none are more emotional than that of Portgas D. Ace. The Summit War at Marineford culminates in his shocking execution at the hands of Akainu; however, other than this sequence, the life of Gold D. Roger's son mostly occurs off-screen.
While a series about Ace's journey as the captain of the Spade Pirates (a topic already explored in the novel, One Piece: Ace's Story) would be a welcome addition to the One Piece franchise, it would also be interesting to see him work his way up the ranks of the Whitebeard Pirates. Considering his untimely passing, a spin-off centered around Monkey D. Luffy's beloved brother would be a great way to honor this memory.
8 Zeff
Although the East Blue is regarded as the most peaceful sea in One Piece, it's still full of experienced pirates that have survived the Grand Line. One such individual is Zeff, the owner of the Baratie, mentor to Sanji, and former captain of the Cook Pirates.
During his time as a pirate, Zeff became fairly well-known, as evidenced by the fact that characters like Don Krieg recognize him decades after he retired from the seas. There's a solid chance that Zeff encountered legendary figures like Gol D. Roger and Monkey D. Garp when he was younger, making the chef's time in the Grand Line a prime candidate for further exploration.
7 Rocks D. Xebec
One Piece has many secrets left to explore in its final saga, yet arguably none are more mysterious than the life of Rocks D. Xebec. The infamous pirate is said to have perished decades before the events of the series, but while he was alive, he rivaled even the likes of Gol D. Roger.
As the captain of the Rocks Pirates, Rocks D. Xebec united powerful individuals such as Charlotte Linlin, Edward Newgate, Golden Lion Shiki, and Kaido under his banner, posing a huge threat to both the World Government and other pirates. The events of Rocks' defeat at the hands of Gol D. Roger and Monkey D. Garp will likely be explained in future arcs, but seeing a series centered around his rise to power would be equally exciting.
6 Rob Lucci
The World Government and the Straw Hat Pirates have clashed on countless occasions, but arguably no single soldier has caused more One Piece's protagonists more issues than Rob Lucci. The assassin serves as a member of CP9 and CP0, and in the Water 7 Saga, he comes extremely close to killing Monkey D. Luffy, only falling short after the pirate unleashes his Gear 3 form multiple times.
As exciting as Lucci and Luffy's battle is, the former earned his notoriety long before he was assigned to capture Nico Robin. While it would require a much darker tone than One Piece, a show following Rob Lucci's missions before and after the Water 7 Saga could be very insightful, especially since there are relevant cover stories in the series' manga to help fill in the gaps.
5 Kong
While most viewers consider the Fleet Admiral to be the highest-ranking authority in One Piece's Marines, there is technically another position that outranks the lofty title — the World Government's Commander-in-Chief. Currently, Kong (who served as Fleet Admiral prior to Sengoku) holds this office, giving him full control of the Marines, Cipher Pol, and several other military branches.
Unfortunately, there is virtually no information about Kong's life, making him one of the biggest enigmas in the entire series. A show focused on his life would be illuminating for several reasons, and at the very least, it could provide some insight as to how he became the World Government's most important military commander.
4 Johnny & Yosaku
Most of the characters introduced during the East Blue Saga haven't appeared in any meaningful capacity since One Piece's two-year timeskip, so there is plenty of reason to revisit the sea where the series began. In fact, two of the most charismatic characters to appear in the saga, Johnny and Yosaku, would be the perfect avenue to explore what has transpired in the East Blue since the Straw Hat Pirates departed.
At some point during the timeskip, Johnny and Yosaku decided to retire as bounty hunters, taking up life as fishermen in Cocoyashi Village instead. Their journey with Roronoa Zoro, as well as their final days as bounty hunters, would be a great, light-hearted way to expand the world-building of One Piece's quietest ocean.
3 Gol D. Roger
A variety of noteworthy characters have appeared in One Piece, but none are nearly as influential as the King of the Pirates, Gol D. Roger. The legendary sailor is the only figure to conquer the Grand Line in the modern era, and if it weren't for a terminal illness, he might still the strongest pirate in the world.
The Straw Hat Pirates uncover many of Roger's secrets during their adventure, providing insight into various moments in his life. However, most of his journey is still a mystery, so many One Piece fans would love to see a spin-off that fills in the blanks regarding his rise to fame.
2 X-Drake
Although there are a few notable exceptions scattered throughout One Piece, Marines and pirates are almost always presented as mortal enemies. The line between the two parties is rarely brought into question, which is a major reason why X-Drake's status as a double-agent is so interesting.
Most characters in One Piece think of X-Drake as a member of the Supernovas, but unbeknownst to them, the Zoan-type Devil Fruit user is actually working as a covert operative for the Marines. Given X-Drake's familiarity with both the pirate world and the Marine hierarchy, a spin-off series focused on his exploits would bring a brand-new perspective to the franchise.
1 Joy Boy
Since Nico Robin and the Straw Hat Pirates first encountered a Poneglyph in Alabasta Kingdom, One Piece has teased the importance of a mysterious time period known as the Void Century. All record of this era has been wiped from the annals of history, leaving only rumors of its most prominent figure — Joy Boy.
Although Joy Boy's exact role in history is still unknown, it's clear that he posed a massive threat to the World Government. As the only individual other than the Roger Pirates to traverse the Grand Line, Joy Boy's adventures must have been comparable to the likes of Roger and Monkey D. Luffy, making him a prime candidate for his own spin-off series.