Setting

The fictional world of One Piece is covered by two vast oceans, which are divided by a massive mountain range called the Red Line. The Grand Line, a sea that runs perpendicular to the Red Line, further divides them into four seas: North Blue, East Blue, West Blue and South Blue. Surrounding the Grand Line are two regions called Calm Belts, which experience almost no wind and ocean currents and are breeding ground for the huge sea creatures called Sea Kings (renamed "Neptunians" in the English manga). Because of this, the Calm Belts are very effective barriers for those trying to enter the Grand Line. While navy ships, using sea stone to mask their presence, can simply pass through, most have to use the canal system of Reverse Mountain, a mountain at the first intersection of the Grand Line and the Red Line. Sea water from each of the four seas runs up that mountain and merges at the top to flow down a fifth canal and into the first half of the Grand Line. The second half of the Grand Line, beyond the second intersection with the Red Line, is also known as the New World.
The currents and weather on the Grand Line's open sea are extremely unpredictable, while as in the vicinity of islands the climate is stable. What makes it even harder to navigate is the fact that normal compasses do not work there. A special compass called a Log Pose must be used. The Log Pose works by locking on to one island's magnetic field and then locking on to another island's magnetic field. The time for it to set depends on the island. This process can be bypassed by obtaining an Eternal Pose, a Log Pose variation that is permanently set to a specific island and never changes.
The world of One Piece is filled with anachronisms, like the transponder snails, snail-like animals that can be attached to electric equipment and function as rotary phones, fax machines, surveillance cameras, and similar devices. Dials, the shells of certain sky-dwelling animals, can be used to store wind, sound, images, heat, and the like and have various applications. A Devil Fruit (renamed "Cursed Fruit" in the edited dub) is a type of fruit which when eaten confers a power on the eater. There are three categories of Devil Fruit. Zoan fruits allow the user to fully and partially transform into a specific animal. Logia fruits give control over and allow the user "to change their living body structure into the powers of nature". Paramecia is a catch-all category for fruits that give the user superhuman abilities. They are said to be incarnations of the Sea Devil himself and as a result, Devil Fruit users cannot swim in sea water as 'they are hated by the sea'. When even partially submerged in sea water, they lose all of their strength and coordination, although some abilities remain, such as Luffy still being able to stretch after being totally submerged. "Moving" water, such as rain or waves, does not have this effect.