The Post-Enies Lobby Arc includes the following characters: the Straw Hat Pirates (Monkey D. Luffy, Roronoa Zoro, Nami, Usopp, Sanji, Tony Tony Chopper, and Nico Robin), Franky, Monkey D. Garp, Coby, Helmeppo, most of the Franky Family members, and Galley-La Company members.
The primary reason for this arc is to deal with the aftermath of the Straw Hats declaring war on the World Government, mainly tidying up remaining character conflicts, such as Usopp's case of returning to the crew. Major events of the arc primarily take place in Water 7, the city of water, as the crew recuperates and readies for their next adventure.
The plot of the Post-Enies Lobby Arc begins with the return of the Straw Hats to Water 7 after their dramatic rescue of Nico Robin from Enies Lobby. Much of the arc revolves around the aftermath of this action at both personal and global levels. One of the central aspects includes the new bounties revealed for the crew members, which reflect the increased threat level against them by the World Government. Luffy, Zoro, and Robin's bounties are considerably raised, while Nami, Usopp under the alias Sogeking, Sanji, and Chopper all get their first bounties. The bounty increases signify an increase in the crew's infamy and consequently, challenges against them.
The arc also deals with the internal conflict within the crew, especially the situation regarding Usopp. After his decision to leave the crew before the events at Enies Lobby, Usopp's return is one of the main emotional focuses. In this storyline, it explores pride, friendship, and how sincere apology works in a group. Indeed, resolving this conflict is key to the unity of the crew as they move into the continuation of their journey.
Another main plot point was Franky's induction into the Straw Hat crew. This should be pegged to having a new ship since the damage that occurred to the Going Merry in escaping Enies Lobby was already beyond repair. Thus, the arc is about both their emotional farewell with Going Merry and their new ship, Thousand Sunny.
The entrance of Monkey D. Garp, a high-ranking Marine and Luffy's grandfather, serves to add real weight to Luffy's past while providing insight into the rest of the One Piece world. He details to Garp, Coby, and Helmeppo how pirates and Marines can have complicated relationships with one another and therefore provides foreshadowing for future conflicts.
There are moments of lightness and character development throughout the arc as the crew recovers from their ordeal and prepares themselves for further adventures. Quiet moments provide the opportunity to reflect upon what happened at Enies Lobby and show signs pointing toward the challenges ahead.
By the end of the Post-Enies Lobby Arc, with Franky onboard as an official shipwright, the Straw Hats were able to sail in their new ship, the Thousand Sunny. Usopp's apology and his eventual reinstatement to the crew marked the end of inner conflict and further tightened the bonds of its members. Increased bounties and the raised awareness of the Straw Hats by the World Government foreshadow much more important clashes in succeeding arcs.
This arc is actually something of a turning point in the One Piece storyline. It closes needed elements from the Enies Lobby arcs, but opens new plotlines and character development. The addition of Franky to the crew, receiving the Thousand Sunny, and resolution of inner conflicts all bring development to the crew as they forge onward.