One Piece is a popular manga and anime series that has been ongoing since 1997. It follows the story of a young pirate named Monkey D. Luffy, who has the ability to stretch his body like rubber, as he and his crew search for a legendary treasure called the One Piece. The series is known for its use of “arcs,” which are extended storylines that introduce new characters and challenges for the protagonists to overcome.

Determining the longest arc in One Piece is somewhat subjective, as different fans may have different opinions on which arc is the longest or which episodes/chapters should be considered part of a particular arc. However, there are a few candidates that could be considered the longest arcs in the series.
One of the most widely recognized long arcs in One Piece is the Dressrosa Arc, which takes place in episodes 629-746 of the anime and chapters 700-801 of the manga. This arc follows the Straw Hat crew as they travel to the island of Dressrosa, which is ruled by the sinister Donquixote Doflamingo. The arc features a complex storyline with multiple factions vying for power, as well as a number of intense battles and emotional moments.
Another possible contender for the title of the longest One Piece arc is the Whole Cake Island Arc, which takes place in episodes 783-877 of the anime and chapters 825-902 of the manga. This arc follows the Straw Hats as they journey to the titular Whole Cake Island, which is ruled by the powerful and manipulative Charlotte Linlin, also known as Big Mom. The arc features several major battles and dramatic revelations about the pasts of several characters.
A third possible contender for the longest One Piece arc is the Wano Country Arc, which is currently ongoing in both manga and anime. This arc takes place in the isolated and mysterious country of Wano, which is ruled by the shogun Orochi and his powerful ally, the pirate Kaido. The arc features the return of several popular characters who had been absent for some time, as well as the introduction of a number of new allies and enemies.
Ultimately, the answer to the question of which One Piece arc is the longest depends on how you define an “arc” and which criteria you use to measure length. However, the Dressrosa Arc, the Whole Cake Island Arc, and the Wano Country Arc are all strong contenders for the title of the longest arc in One Piece, and all have their own unique strengths and memorable moments. Whether you’re a long-time fan of the series or just getting started, there’s sure to be an arc in One Piece that will capture your imagination and keep you coming back for more.