One Piece is one of the longest-running anime series of all time. The series started airing in 1999 and since then it has released over a thousand episodes. While many people are reluctant to start watching it as they tend to think that it is too long, avid fans think the anime is too short.
The anime has many arcs and all of them offer incredible entertainment. The number of episodes per arc varies, and sometimes when a person wants to re-watch a specific arc, they have to sit through a lot of episodes as the anime tends to add content of its own, which makes it difficult to rewatch an arc. So, a movie that covers a specific arc can act as a time saver, especially if the movie adapted one of the longer One Piece arcs.
6 Whole Cake Island
The Whole Cake Island is one of the best arcs since the time skip. Luffy's group decided to sail to Whole Cake Island to get back Sanji from the clutches of Big Mom. Sanji was being used by the Vinsmoke Family to cement an alliance with Big Mom, but Luffy wasn't ready to let go of his beloved crew member. So, he decided to set sail to the Yonko's territory and confront Sanji.
The arc has a total of 95 episodes, making it one of the longest arcs in the series. The arc delved into the past of Big Mom, and it also explored the dark history of Sanji and the other members of the Vinsmoke Family. If this arc was turned into a movie, it would have made the arc easily watchable for those who don't have enough time to watch it again. The movie adaptation would have also added more details to the fight between Katakuri and Luffy. The Straw Hats leaving the territory of the Yonko would have acted as the perfect ending to the movie.
5 Wano Country Arc
Undoubtedly, the Wano Country arc is the best arc in the series so far. After the Straw Hats left Big Mom's territory, they made their way to Wano where they would face the King of Beasts, Kaido. While the arc is almost over in the manga, there is still some time left before the anime is done with the arc.
The Wano Country arc is over a hundred episodes long. The arc is definitely fascinating, and the animation quality has been better than most arcs. A movie adaptation covering the arc would be quite long, but it would allow the fans to go through the story much quicker. The movie would be fast-paced, and it would have plenty of fights, which would make it a great watch.
4 Dressrosa
The Dressrosa was the first arc after the time skip, where the Straw Hats were in genuine danger. After forming an alliance with Trafalgar Law, Luffy, and co. headed to the island of Dressrosa to take down Donquixote Doflamingo. Unfortunately, the Straw Hats had to split up, but that did not stop the arc from being amazing.
The arc showcased the true nature of Doflamingo and how he managed to take over the country of Dressrosa. In addition to having the return of Sabo, Luffy's Gear Fourth also debuted in the arc. The arc has a whopping 118 episodes, which is not a small number by any means. It does feel dragged out sometimes, so a movie would be a much better fit.
3 Fishman Island
The Fishman Island arc is often overlooked in debates regarding the best arcs, however, it is unquestionably one of the most important arcs in the series. The Straw Hats visited Fishman Island after they left Sabaody Archipelago. While the arc did not feature any powerful enemies, it tackled some crucial themes.
The Fishman Island arc showed how prevalent racism is in the world of One Piece. The hatred between Fish-men and humans was saddening to watch. The arc has just over 50 episodes. If the arc received a movie adaptation, it could put a bit more stress on the themes of the arc, because many fans tend to overlook it during the first watch.
2 Loguetown arc
The Loguetown arc holds a lot of significance in the story. It is the final arc in the East Blue Saga, and it is the last place that the Straw Hats visit before setting sail for the Grand Line. The arc introduces two new characters, who are important to the story. These are: Smoker, a Navy captain, and Monkey D. Dragon, the leader of the Revolutionary Army.
The arc is set in Loguetown, which is the place where Gol D. Roger was executed. In the arc, Luffy finds himself on the brink of death, and just like the Pirate King, the young pirate smiles while facing certain death. The arc is 7 episodes long, which can be turned into an adequately timed movie.
1 Enies Lobby arc
The Enies Lobby arc is among the best arcs in the series. It focuses on the Straw Hats and their battle with the CP9. The Straw Hats followed CP9 to Enies Lobby as they wanted to rescue Robin from their clutches. After Robin declared her wish to live, the Straw Hats started their fight against the CP9.
When all the Straw Hats successfully managed to defeat the members of the CP9, they finally escaped from Enies Lobby and gave the Going Merry a proper send-off. A movie about the Enies Lobby arc would be perfect as it would allow the fans to relive some of the best moments in the series without going through 41 episodes.