Kairoseki (海楼石 Kairōseki, translated as "Seastone"; literally meaning "Sea Watchtower Stone"), is a naturally occurring (though apparently rare) substance that can cancel out Devil Fruit powers and weaken Devil Fruit users. The Marines appear to have vast quantities of it, using it for jail cells, handcuffs, weapons, and the bottoms of battleships. It is only located on the Grand World.
Seastone is said to give off "a wavelength that is the same as the sea itself", leading to it to be identified as a solid form of the sea. So far the material has only shown effect upon actual contact with someone who has eaten a Devil Fruit. Upon contact the material drains the victim's body of energy, and negates their Devil Fruit powers - having the same effect as throwing them into the sea.
The degree of "weakness" induced by the Kairoseki depends on its density and composition; for example, Kairoseki handcuffs rob the prisoner of their abilities, but still allow the prisoner to walk around normally. Kairoseki only works upon direct and constant contact, presumably, thick clothing will prevent the Kairoseki's effect from harming the victim.
However, it has been shown that though a Devil Fruit user loses his powers when in contact with the Kairoseki, said powers can still be used on the Kairoseki.
The effects of Kairoseki also affect creatures of the sea such as Sea Kings. By layering the bottom of the ships with Kairoseki, creatures that are underneath the ship will be unaware of the vessel, and thus will not attack it. However, while the Kairoseki hides the movements of the vessel traversing above the Sea Kings, that does not mean they still cannot see the ship. Kairoseki is harder to break than diamond.
An element contained in the Kairoseki called pyrobloin forms the special clouds (Sea Clouds or Island Clouds, depending on the density of the water) of the sky islands when they absorb water.
Typically, Kairoseki is primarily found in the form of restraining devices, such as shackles or cages, but they have other uses. Thus, it is deployed as a Devil Fruit counter by the Marines as well as other groups like the Shichibukai and Cipher Pol. Some devices are adapted so the Marines with Devil Fruits can use these weapons, without actually making contact with the device themselves, an event which would nullify their own powers in the process of trying to handle another with a Devil Fruit ability.
- Bullets: These bullets not only wound Devil Fruit users, but also rob them of their strength and their ability to use their powers until they are extracted, making them very effective weapons.
- Kairoseki Net: A net made of Kairoseki. When thrown on a Devil Fruit user, it prevents the use of their powers.
- Kairoseki Cage: The Government's central prison, Impel Down, uses Kairoseki cages.
- Kairoseki Cuffs: A special handcuff made to arrest those with Devil Fruit powers. The lock is made of Kairoseki so that when a Devil Fruit user is wearing them, they cannot use their powers, but unlike other Kairoseki, it does not inhibit their mobility.
Other Uses Edit
- Marine Ships: Kairoseki can mask the presence of a ship from Sea Kings and other sea-dwellers, and therefore had the bottom of Marine ships covered in a layer of it, which is especially useful when traveling across the Calm Belt. However, the Sea Kings can still see the ship, so it is not an absolute protection.