The East Blue Saga is the first storyline of both the manga and anime adaptation by Eiichiro Oda based on his series One Piece, covering 1-100 chapters of the manga and episodes 1-61 of the anime. This saga set up the general setting of the world of One Piece and introduced the main characters who would later become Straw Hat Pirates members.
This saga is divided into six main arcs: Romance Dawn, Orange Town, Syrup Village, Baratie, Arlong Park, and Loguetown. Each of these arcs serves to properly develop the main protagonists and further advance the world of One Piece.
The Romance Dawn Arc introduces the main hero of the story, Monkey D. Luffy, who is to become a Pirate King. This arc reveals his special ability through eating a Devil Fruit known as the Gomu Gomu no Mi, which makes his body rubber. This arc also introduces Roronoa Zoro, a swordsman with the dream to become the greatest in the world, who becomes Luffy's first crew member.
Orange Town introduces the legendary navigator Nami, who has a dark past, and provides the first major villain in the series—Buggy the Clown. Buggy himself used to be one of the crew members of the former Pirate King, Gol D. Roger. He consumed the Bara Bara no Mi, known as the Chop-Chop Fruit in English, allowing him to split his body into pieces.
The Syrup Village Arc is when the crew meets Usopp, the sharpshooter and compulsive liar. It introduces the concept of "Klahadore" and the Black Cat Pirates, captained by Captain Kuro, known for his cat claws and superhuman speed.
The Baratie Arc introduces into the crew one Sanji, a skilled cook by profession and a chivalrous knight by nature. This is also where the first appearance of Dracule Mihawk, one of the Seven Warlords of the Sea, happens, establishing once and for all the power gap between the East Blue and that of the Grand Line.
The Arlong Park Arc is one of the high points in the saga of East Blue. It focuses on Nami's past and introduces racism with the Fish-Man pirates under Arlong's leadership. This arc has Luffy's classic "Gomu Gomu no Ono" attack, which destroys Arlong Park.
The saga is concluded finally with the Loguetown Arc, set in the town where Gol D. Roger was born and executed. It introduces vital characters like Marine Captain Smoker and the Revolutionary Dragon and hints at larger conflicts to come.
Within the East Blue Saga, Oda introduces key concepts that later become integral parts of the series. One of the ongoing themes is the Devil Fruit; it gives one special powers beyond human capabilities but forbids the bearer from swimming. It is through the many talents of these characters that he explores the potentials of the fruits' powers. Another mysterious power is Haki, alluded to little in the story at this point, not fully explained until far into the series.
The East Blue Saga also presents the main members of the Straw Hat Pirates: Luffy, Zoro, Nami, Usopp, and Sanji. This would bring some richness to each character's introduction into the crew while developing themes of friendship, loyalty, and following one's dreams.
It is quite influential in world-building, featuring Four Blues, which are East Blue, West Blue, North Blue, and South Blue, as well as the notorious sea known as the Grand Line, which splits the world in two. Likewise, there are the Shichibukai, which literally translates to 'Seven Warlords of the Sea,' and the Marines who set up powerful figures for complex power dynamics that define One Piece.
It also sets up several plot points and character arcs in the East Blue Saga. For example, Zoro's ambition to be the world's greatest swordsman was established after he lost to Mihawk. The mystery of the Will of D was subtly introduced with Luffy's full name, Monkey D. Luffy.
The anime adaptation of the East Blue Saga contains iconic musical themes associated with some characters and situations. One example would be Luffy's theme, "Overtaken," which plays often at very pivotal moments, really adding so much more emotion to key scenes.
Loguetown marks the end of the East Blue Saga, symbolically closing off the "prologue" into One Piece and setting the stage for the larger-than-life adventures that await in the Grand Line. As the Straw Hat Pirates set sail for the Grand Line, so viewers and readers are primed for the escalating challenges and expanding world defining the following sagas of One Piece.