Sea King

Sea Kings (known as Neptunians in the English manga) are sea monsters in the anime and manga One Piece, which are generally much larger than normal sea creatures. They are found in great numbers along the Calm Belt around the Grand Line, although in rare occasions they can be found in other places throughout the world.

Sea Kings make trade and travel difficult for anyone trying to cross the water where they are found. Cases have arisen where some islands in the Grand Line close to the edge of the Calm Belt (their natural breeding ground) have ended up getting almost completely cut off from the rest of the world. In Water 7 and its surrounding islands, this led to the eventual creation of the Sea Train as a means to travel safely to and from each of its surrounding islands.

Sea Kings are serpent-like in appearance, however they vary from one Sea King to another in exact appearance and size. Some may have arms and legs and one particular sea king even was note to look like an oversized frog. Only the strongest of ships or captains can take on a Sea King. Most other creatures in the ocean fear the Sea King, with the notable exception of Bananawani (their only natural predator), Yuda (who are too ferocious even for them), Blue Gorillas ( Impel Down guards who are extreamly good swimmers and super strong), and Giants (who are incredibly strong themselves). Confrontation with one by all but a few humans is inadvisable and is considered nothing short of suicide. Many characters, such as Franky, see the act of killing one a sign of strength and achievement.

Very few Sea Kings end up with names, only those who commonly inhabited the same waters receive names. The Sea King that ate Shanks' arm is known as The Lord of the Coast, and Long Ring Long Land Island had a Sea King called Master of the Waters.