A Klabautermann is said to be a water spirit (or fairy) that dwells on ships and is basically an incarnation of a ship that has been well cared for. 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.
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 cares for their ship.
Sky Island Arc
The Klabautermann of the Going Merry was first seen during the Skypiea Arc, when Usopp saw it fixing the heavily damaged ship, and it told him that it would strive to sail the crew farther for a little while longer.
Water 7 Arc
It was spoken of briefly by Franky after he had kidnapped Usopp, who had temporarily left the Straw Hat crew. He identified the Klabautermann and described it as 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 at Skypiea. Franky then revealed that if the ship were to sink with Usopp still onboard, the Klabautermann would not be able to go to Heaven, much to Usopp's further grief.
Enies Lobby Arc
When Iceburg recounted how he encountered the Going Merry during Aqua Laguna, the Klabautermann was shown speaking to him, pleading to go out to sea one last time, and this convinced him to make the ship seaworthy before the Aqua Laguna carried it away. The Klabautermann of the Going Merry spoke to the Straw Hats to call them to her at Enies Lobby and again at the Going Merry's viking funeral.
Episode of Merry
During Episode of Merry, a Klabautermann (presumably Merry's) made an appearance again briefly on the Thousand Sunny. It was sitting above the sails, watching the Straw Hats and smiling. Usopp saw it briefly as it disappeared, and shed a tear of reminiscence of the old ship he loved so much.
Concludes non-canon section.
- 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 itself.
- In real world myths, Klabautermann 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. The word Klabautermann comes from older dialects of the German language.
- There is also one bad omen associated with it. The spirit 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.
- One Piece Manga and Anime — Vol. 37 Chapter 351 and Episode 247, Franky explaining to Usopp about the Klabautermann
- One Piece Manga and Anime — Vol. 27 Chapter 254 and Episode 167, Usopp seeing the Klabautermann
- One Piece Manga and Anime — Vol. 44 Chapter 430 and Episode 312, The Going Merry's funeral
- Klabautermann – Wikipedia article about the water sprite in real-life legends.