One Piece

The world of One Piece is populated by humans and several human-like lifeforms, including mermen and mermaids; "fishmen", fish-human hybrids; and giants. It is covered by two vast oceans, which are divided by a massive mountain range called the Red Line (赤い土の大陸（レッドライン） Reddo Rain^?).^[4] The Grand Line (偉大なる航路（グランドライン） Gurando Rain), a sea that runs perpendicular to the Red Line, further divides them into four seas: North Blue (北の海（ノースブルー） Nōsu Burū), East Blue (東の海（イーストブルー） Īsuto Burū), West Blue (西の海（ウェストブルー） Uesuto Burū) and South Blue (南の海（サウスブルー） Sausu Burū).^[5] Surrounding the Grand Line are two regions called Calm Belts (凪の帯（カームベルト） kāmu beruto), which experience almost no wind and ocean currents and are breeding ground for the huge sea creatures called neptunians (海王類 kaiōrui, lit. "sea kings"). Because of this, the calm belts are very effective barriers for those trying to enter the Grand Line.^[6] While marine ships, using sea-prism stone (海楼石 kairōseki) to mask their presence, can simply pass through,^[7] most have to use the canal system of Reverse Mountain (リヴァース・マウンテン Rivāsu Maunten), 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.^[8] The second half of the Grand Line, beyond the second intersection with the Red Line, is also known as the New World (新世界 Shin Sekai).^[9]
The currents and weather on the Grand Line's open sea are extremely unpredictable, whereas in the vicinity of islands the climate is stable.^[10] What makes it even harder to navigate is the fact that normal compasses do not work there.^[11] A special compass called a Log Pose (記録指針（ログポース） Rogu Pōsu^?) must be used.^[12] The Log Pose works by locking on to one island's magnetic field and then locking on to another island's magnetic field.^[13] The time for it to set depends on the island.^[14] This process can be bypassed by obtaining an Eternal Pose (永久指針（エターナルポース） Etānaru Pōsu), a Log Pose variation that is permanently set to a specific island and never changes.^[15]
The world of One Piece is filled with anachronisms, like the Transponder Snails (電伝虫 Den-Den Mushi^?), snail-like animals that can be attached to electric equipment and function as rotary phones,^[16] fax machines,^[16] surveillance cameras,^[17] and similar devices.^[17] Dials (貝（ダイアル） daiaru), the shells of certain sky-dwelling animals, can be used to store wind, sound, images, heat, and the like and have various applications.^[18]
A Devil Fruit (悪魔の実 Akuma no Mi) is a type of fruit which when eaten confers a power on the eater.^[19] There are three categories of Devil Fruit.^[20] Zoan (動物系（ゾオン） Zoon) fruits allow the user to fully and partially transform into a specific animal.^[21] Logia (自然系（ロギア） Rogia) fruits give control over and allow the user "to change their living body structure into the powers of nature".^[20] Paramecia (超人系（パラミシア） Paramishia) is a catch-all category for fruits that give the user superhuman abilities.^[22] 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".^[23] 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.
Haki (覇気^?, lit. "Ambition") is an ability every living being in the world of One Piece possesses. It comes in three varieties: Color of Observation Haki (見聞色の覇気 Kenbunshoku no Haki) allows to sense the presence of other beings and predict their movement, Color of Arms Haki (武装色の覇気 Busōshoku no Haki) allows one harden one's body, and the rare Color of the Supreme King (覇王色の覇気 Haōshoku no Haki) enables one to render beings of weak determination unconscious.