"Soul King" Brook is the musician of the Straw Hat Pirates. He is a skeleton that the Straw Hats found on board of a ghost ship after drifting into the Florian Triangle. He is a Devil Fruit user who ate the Yomi Yomi no Mi, and is undead, having been brought back into a pseudo-immortal state because of its powers. He is the ninth member of the Straw Hat crew, and the eighth to join Luffy's crew, as well as being the oldest member on board. He is also one of the two swordsmen onboard their current ship, with the other being Roronoa Zoro. He fills the role of the long-awaited musician that Luffy had wanted for his crew ever since his journey began. He currently has a bounty of Beli83,000,000. As much as Brook normally goofs around on the ship engaging in acts of silliness with Luffy, he is still a formidable opponent.
Due to his previous experiences and skills that he amassed from the days when the Pirate King, Gol D. Roger was still active, Brook, in all respects, is a veteran pirate (though these attributes are somewhat downplayed by his overall demeanor, along with the fact that his isolation in the Florian Triangle seemed to have eroded his knowledge of modern society). Though he often gets scared easily by powerful enemies or the supernatural, he can be very calm and fearless to defend his crew. Examples are such as when he cleverly realized he could trick Jora to defeat her, and when he willingly sacrificed himself hoping to hold back Kuma. Brook's value to the crew was already evident during the Thriller Bark Arc, where he proved indispensable for the Straw Hats on their encounters with the island-vessel's many undead inhabitants. Brook is a musician who is able to play any musical instrument. He usually uses a violin to play his music, though after two-years he switched his main instrument to a guitar. His musical abilities are so good that Laboon used to sing along to his music when they were together. When Brook fights, his battles often have a comical element to them. Examples include making a few of the members of his own crew fall asleep while fighting the Flying Fish Riders, playing dead halfway through a battle, or launching himself at an enemy with erroneous results. Brook also has somewhat good endurance, as he was able to remain conscious after Bartholomew Kuma used his Ursus Shock on Thriller Bark, however he could not get up or he simply decided not to. After the timeskip Brook's overall skills have proven to be a very important asset during battle. However, his childish personality somewhat hampers his effectiveness. He has grown significantly in physical strength, as he is now able to launch a flying slash strong enough to break through thick ice, and can also block a thrown, weighted chain from a steroid-enhanced fishman. Brook's devotion to music not only helped him to pass the lonely days during his long isolation, but also serves as a combat tool. His technique, "Nemuriuta Flanc", loosely translated as "Lullaby Parry", shows this, where he strums his violin with his shikomizue like a violinist's bow, creating a soothing tune that makes anyone who hears it immediately fall asleep. Due to his musical background, Brook also moves according to the rhythm of his music to assist him in battle. His musical skill is such that he became a world famous rock star during the two years the Straw Hats were separated; his records in Tone Dials selling in the millions and his fans during his final world tour stop in Sabaody Archipelago were either crying or fainting at his presence.
His music also shows capabilities to change its listener's attitude and emotions such as when he was sent to the Namakura Island by Bartholomew Kuma his music inspires the cult there to fight back against its invaders, the Longarm Tribe. During the fight with the New Fishman Pirates, Brook revealed that he has developed his musical ability to the point where he could completely change the mood and hypnotize his opponents to believe they were at a festival. His opponents believed the illusion was reality and ended up using their cannons as fireworks. Since he is a musician, he has great hearing abilities, as he was able to detect where Zeo was, while he was invisible, even though it was shown to be difficult to figure out where he was based on sound. While he was still alive, Brook ate the Yomi Yomi no Mi, a Paramecia-class Devil Fruit. Should the user of this fruit die, it allows them the one-time opportunity to return to life. Though his soul was not able to find his body in time before it decomposed completely to a skeleton, he gained some advantages that would otherwise be impossible to do without being a skeleton supported by Devil Fruit powers. One advantage is that because he is just comprised of light weighted bones, he can use his speed and light weight to run across water, but, like all Devil Fruit users, he can still drown when submerged. With the aid of his powers, he is also able to function like a regular human being, and retains all the strength he had when he still had actual muscle mass. He is able to perform normal acts such as drink, eat, cry, digest, and even "poop" normally. He has also proven that calcium (such as in milk) will rapidly heal any damaged bones. Due to his light-weight skeleton body, he can leap great distances, jump very high and run so fast that he can even run on water without sinking, and can also store things in his skull cavity such as a Tone Dial. His skeletal appearance not only gives him immense amounts of agility on par with Zoro and Sanji, but the fact that he does not have body parts allows him to take less damage in a manner of speaking, as he does not have the physical limitations of a normal human. His bone regeneration from milk also allows him to heal a lot faster than the rest of the crew, effectively making him one of the most tenacious opponents in battle. Due to his agility, he has managed to leap close enough to a firing harpoon and destroy it with his sword, while the harpoon was in flight, with relative ease. Due to being entirely made of bones, he appeared to be resistant against lightning and electricity in general. Furthermore, Brook appeared to be resistant against the deadly poison of Shinokuni, however gases that enter the body through one's respiratory system such as KYP and the unnamed sleeping gas that Caesar's men used still affect Brook normally. Due to all of his flesh having rotted off, he also no longer suffers from aging, and therefore is immune from senescence, being nearly a century old without showing the ill-effects of the elderly. After the timeskip, it is revealed that he can separate his spirit to move individually of his body similar to Perona, but is unable to move while in this state. During his battle with Zeo, Brook recalls how in the last two years, he discovered the true power of his devil fruit, and how he is no longer animated by organs or bones, but by his spirit. Brook is also shown to be capable of reattaching his head in the event it is pulled off, and according to the skeleton, as long as his bones are not broken, his core remains unharmed, which will allow him to reconstruct his body.