The Dressrosa Saga is the eighth major storyline in the One Piece manga and anime series by Eiichiro Oda and the second saga of the New World Arc. This saga includes two different arcs: the Punk Hazard Arc and the Dressrosa Arc, the latter being the focus and one of the longest arcs in the series.
The Dressrosa Arc, which makes up most of this saga, is the longest in One Piece as of its release, covering 102 manga chapters and a record 118 anime episodes. Set on the island kingdom of Dressrosa, it is ruled by one of the Seven Warlords of the Sea, Donquixote Doflamingo. The culture of the island is unique, inspired by Spain, with living dolls cohabiting with humans as a facade that conceals a reality of oppression and manipulation.
At the core of the storyline is the alliance of the Straw Hat Pirates with Trafalgar Law against the power of Doflamingo, who disturbs the production of artificial devil fruits called SMILEs. In this way, it adds a new dynamic to the series: how pirate crews relate to and interact with each other in the New World.
The saga introduces a number of major characters, including Fujitora, who is a new naval admiral with powers related to gravity manipulation. This challenges the more conventional naval view of absolute justice. Other major introductions include the Tontatta tribe and the gladiators of the Corrida Coliseum, which include fan favorites like Bartolomeo and Cavendish.
A major plot element includes the Corrida Colosseum Tournament, in which fighters participate to win the Mera Mera no Mi, otherwise known as Flame Fruit, formerly belonging to Ace, Luffy's brother. This creates a tournament arc inside the saga, allowing many new characters to be introduced while showing grim fights that convey the vast diversity of fighting styles existing in the world of One Piece.
The Dressrosa Saga has a very profound backstory on Doflamingo and the Donquixote family, filled with complex political intrigue, family drama, and the dark past of the World Nobles. This exposition adds depth to the world of One Piece and reveals the reasons behind the present power dynamics in the story.
Another major important aspect of the Dressrosa Saga is the perspective for the expansion of Luffy's influence across the New World. Indeed, it is what happened in Dressrosa that gave rise to the formation of the Straw Hat Grand Fleet, which united seven pirate crews under Luffy's leadership. This changed so much Luffy's status as a pirate and became a foreshadowing marker of events for his importance in the world of One Piece.
The saga also furthers the plot of One Piece in general, revealing more about the Will of D and the Void Century, as well as the Ancient Weapons. The presence of the Tontatta tribe related to the Skypiea dwarves further thickens this series' mythology.
Taking the Dressrosa Saga as a case study on combat action, there has definitely been a notable improvement of the Straw Hats compared to their respective skills from before the two-year time jump. With Luffy's introduction of Gear Fourth, viewers are granted a view of how much he has improved since becoming a warrior. Other crew members, mainly Zoro and Usopp, increase their power really but visibly.