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- North Blue is the northernmost ocean of the Blue Sea and is the birthplace of such figures as Sanji of the Straw Hat Pirates, Trafalgar Law of the Heart Pirates, and the famous explorer, Mont Blanc Noland.
- South Blue is the southernmost ocean of the Blue Sea and the ocean from which the St. Bliss sailed on its ill-fated voyage to Skypiea. Franky, Eustass Kid, Inazuma, and Portgas D. Ace all are from South Blue.
- East Blue is the easternmost ocean of the Blue Sea and the birthplace of Pirate King Gol D. Roger, Monkey D. Luffy, Monkey D. Dragon, and Roronoa Zoro. Notable islands in the East Blue include Loguetown, Dawn Island, and Shells Town.
- West Blue is the westernmost ocean of the Blue Sea and once contained the island of Ohara prior to its destruction by the World Government. Notable figures from the West Blue include the Yonko Shanks, Nico Robin and Brook.
- Grand Line is the part of the Blue Sea enclosed by the Calm Belts. It is divided into two parts by the Red Line. The first half is known by those who have been to the second half as Paradise. The second half is known as the New World.
The main governmental body of the Blue Sea is the World Government which currently exercises control over a hundred-seventy countries. The Revolutionary Army is the main force opposing the World Government and they control multiple islands including Baltigo and Momoiro Island. The Yonko are the four strongest pirates who rule over the New World.
Moving from one section of the Four Blues to another is no easy task, as they are separated by the Red Line, which would entice a full-voyage to go through.
- ↑ One Piece Manga — Vol. 81 Chapter 813 (p. 4-5), Brook notes that Sanji moving from North Blue to East Blue is something big.