About the Skypiea Arc
The Straw Hats arrive on the Sky Island Skypiea and learn of its connections to Jaya and Mont Blanc Noland's tale of a lost city of gold. As the crew embarks in search of treasure, they become entangled in a three-way war between the native Skypieans, the vengeful Shandians, and the land's cruel "god", Enel.
Having ridden the Knock Up Stream, the Straw Hats find themselves in a sea of clouds (which, as they find out, has the same effect as normal water on a Devil Fruit user), but before they have a chance to relax, they are quickly attacked by a strange man in a mask who is riding on the clouds. The crew are unable to defend themselves, but they are thankfully saved by an old knight named Gan Fall, who rides on a bird with Devil Fruit powers named Pierre. He points out to them that the reason that they could not fight back against the "Guerrilla" was due to the thin air, though immediately afterwards the crew says that they are starting to get used to it. Gan Fall gives them a whistle to summon him in case they run into more trouble, and the crew continues on.
They reach "Heaven's Gate," the entrance to Skypiea, where they are told to pay 1 billion Extols per person as the entrance fee, but the crew has no idea what an Extol is. In response, the gatekeeper, Amazon, basically tells them she does not care what they do but does not warn them that if they pass without paying, they will be marked as criminals, and the crew goes into Skypiea.
The ship reaches the shore of Angel Island, the main part of Skypiea, where they meet a girl named Conis and her father, Pagaya. They let the crew come into their house so they can introduce them to Skypiean society, but Nami decides to stay at the ocean and try out Pagaya's Waver, a device similar to a jet ski that can move under its own power without any wind. While Conis explains the use of Dials, Nami ends up riding the waver to a nearby island with a huge forest. When Sanji points out that Nami is gone, Conis and Pagaya explain that the nearby island is known as Upper Yard. Upper Yard is a forbidden sacred ground where God Enel and his priests reside, and no one must ever set foot on it. This immediately sparks Luffy's interest, and he commands that they head out to "rescue Nami," but he makes it obvious that he simply wants to go to Upper Yard to explore and have an adventure.