Seastone (Sea-Prism Stone) is a naturally occurring (though apparently rare) substance that can drain the energy of Devil Fruit users to the point where they can't consciously control their powers. Dr. Vegapunk has invented revolutionary ways to use this rare substance. The Marines appear to have vast quantities of it, using it for jail cells, handcuffs, weapons, and the bottoms of battleships.
It is stated by Pagaya that Seastone contains a compound known as Pyrobloin which when separated from Seastone can help to create Island Clouds or Sea Clouds.
Seastone is as hard as diamond, meaning that one cannot simply break them.
Effects on Devil Fruit UsersEdit
Effects on Lost MagicEdit
Typically, Seastone 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 Seven Warlords of the Sea 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.
- Nanashaku Jitte: Smoker's jitte, where the tip is made of Seastone, so Smoker can use it to nullify his opponent's Devil Fruit powers.
- Seastone Net: Used in Loguetown, a net made of Seastone was thrown on Buggy and Alvida completely preventing them from using their powers. Alternatively, it was used to capture Monkey D. Luffy, Buggy, and Mr. 3 in Impel Down, but the Sphinx tore it apart, indicating that only parts of the net contain Seastone, while the rest is steel cable.
- Seastone Cage: Seen in Alabasta, it was used by Crocodile to drain Luffy and Smoker's powers and make them unable to use their Devil Fruit abilities. The Government's central prison, Impel Down, also uses Seastone cages.
- Seastone Cuffs: A special handcuff made to arrest those with Devil Fruit powers. The lock is made of Seastone so that when a Devil Fruit user is wearing them, they cannot use their powers, but unlike other Seastone, it does not inhibit their mobility. During the Enies Lobby raid, Nico Robin wore them until Sogeking delivered the key to the bridge. Despite being unable to use her powers to fight back, she was able to move, and could attempt to escape or otherwise resist being taken to the Gates of Justice. Sogeking tried to throw Seastone handcuffs at Jabra and Kaku in order to prevent them from using their Devil Fruit powers and make them easier to defeat, but got distracted by Kaku's "square" giraffe face and accidentally threw them on Zoro's wrist, and got handcuffed to him while also ducking due to Kaku's Amanedachi. These were also hooked onto Ace's arms and legs in his prison cell in Impel Down to prevent him from using his Devil Fruit powers. Onigumo also clasped one onto Marco during the war in Marineford, to nullify his Devil Fruit powers. Usopp fired a pair of Seastone shackles to coil around Caesar Clown's neck, disabling his Gas-Gas Fruit ability.