Klabautermann

Klabautermann (クラバウターマン) is said to be a water spirit (or fairy) that dwells on ships that are well cared for and is basically an incarnation of the ship. It is a merry and diligent creature that is said to warn sailors when a ship's in danger and help in bigger ways sometimes. They are normally considered to be only a legend among seafarers.

Appearance
A Klabautermann resembles a small humanoid sailor wearing a sailor's raincoat and a pair of shoes, and carries with it a small wooden hammer. The human form of a Klabautermann only reveals itself to someone that truly cared for their ship.

History
The Klabautermann of the Going Merry was first seen during the Skypiea Arc, when Usopp saw it fixing the heavily damaged ship. The sharpshooter of the Straw Hat pirates overheard the Klabautermann telling the Going Merry that it would strive to sail the crew farther for a little while longer.

It was spoken of briefly by Franky when he had kidnapped Usopp after he had temporarily left the Straw Hats crew. He revealed that a Klabautermann is a manifestation of a ship's soul brought about when it has been loved and cared for enough by its owners. Usopp then realized that it really was Merry who had spoken to him in Skypiea. It can be said that it was the Klabautermann of the Going Merry that spoke to the Straw Hats at the Going Merry's viking funeral.

Trivia

 * Strangely enough, despite not making much of an appearance, the Klabautermann was ranked as the 49th most popular character in the series (with 46 votes), 2 votes more than the Going Merry herself.
 * In real world myths, it is said to be a male seafaring spirit that aids ships of crews that truly deserve it, rather than being an incarnation of the ship.
 * There is also one omen associated with it. That it only makes itself visible to the crew of a doomed ship. This is shown to be true in One Piece, as Usopp saw the spirit fixing Going Merry back in Skypiea, and in the end, due to various events occurring, Going Merry was broken beyond repair and had to receive her Viking Funeral.