Kimimaro was one of Orochimaru's most powerful followers. He was the last surviving member of the Kaguya clan and later became the leaser of Orochimaru's Sound Four, making the Sound Five.
Kimimaro was born into the Kaguya clan as a rare holder of the clan's kekkei genkai, Shikotsumyaku, which allows its users to manipulate their bone structure as a weapon. Having this caused even his own clan, who loved murder and battle, to fear him, and they kept Kimimaro locked away for most of his young life, releasing him only to fight for the clan when needed. Kimimaro's father, the Kaguya clan patriarch, released him one time to help fight against Kirigakure, one of the mighty shinobi villages who they felt had betrayed them. Along the way, Kimimaro enountered Zabuza Momochi and Haku, an S-rank Missing-nin of the village and his apprentice, who he passed by after they denied connection to Kirigakure, and later encountered his soon-to-be master, Orochimaru, an S-rank Missing-nin of Konohagakure, who showed him to his destination. After reaching the village, his clan, having underestimated their opponent's defenses, were all wiped out after a long battle, with only Kimimaro surviving. Wandering aimlessly, Kimimaro was eventually found by Orochimaru, who took him under his wing and made him into one of his most powerful followers. Kimimaro, on one occassion, found and brought Jugo, a boy with strange, rage-connected chakra tranformation powers nearly identical to Sage Mode, and brought him back to Orochimaru, who he believed could help his rage issues. Kimimaro went on to form a good friendship with Jugo that lasted until his death. Kimimaro went on to be granted with the Cursed Seal of Earth from Orochimaru, which he developed, along with others variants, from Jugo's DNA and branded all of his strongest followers with. With this at his command, Kimimaro went on to defeat the Sound Four, orochimaru's bodyguards, and become their leader, threatening to kill them if they didn't obey him. Orochimaru came to view Kimimaro as his ideal vessel, desiring to take him for his new body, something Kimimaro was very proud of and looked forward to. By the time of Orochimaru's invasion of Konohagakure, Kimimaro helped him to gain disguise bodies for the Chunnin Exams, at which point he gave a bloody cough, which he disregarded. He later helped Orochimaru in his successful assault on the Fourth Kazekage, who Orochimaru murdered. Kimimaro then finally fell ill to his fatal disease, forcing Kabuto to put Kimimaro into extreme medical care and sleep to keep him alive for as long as possible.
Kimimaro made his debut in part 1 of the series being awoken by Kabuto Yakushi, who told him of his master, Orochimaru's great pain and how it would eventually destroy. Continuing to ask Kimimaro what he thought his purpose was, he came up with the answer that it was to find Sasuke Uchiha and bring him to his master as his new vessel, stating it would give his existence some value. On his way, Kimimaro visited his olf friend, Jugo, at his cell and told him Sasuke was his ideal vessel, before continuing to find his subordinate, Tayuya, who he ordered to kill Shikamaru Nara and Naruto Uzumaki, before leaving with the coffin containing Sasuke he had taken from the Konohagakure Gennin. However, Naruto eventually made his way to him, and Kimimaro was forced to use his Dance of the Camellia technique to create a steel-hard bone sword, which he used to destroy the hundreds of Kurama-enhanced shadow clones Naruto created. As Sasuke then broke out of his coffin, Kimimaro attempted to kill Naruto when he let down his guard, but was kicked away by Rock Lee, another Konohagakure shinobi, who allowed Naruto to leave. Though he saw Lee as a stronger opponent than Naruto, Kimimaro easily proved to be more than a match for him at first, but after the latter drank some sake, thinking it was his medicine, and began to use the Drunken Fist taijutsu art, Kimimaro was rendered unble to read his unorthodox movements and was struck down. Impressed and admitting his inability to read Lee, Kimimaro partly activated his Cursed Seal of Earth's first stage and used his Dance of the Larch technique to fight Lee and eventually managed to cut him, sobering Lee up. With the advantage once again his, Kimimaro easily overcame lee and struck him down. As he started to leave, however, Lee got up and tried to use his Front Lotus move against Kimimaro, who caught Lee's kick with his bones.
Praising Lee's speed, Kimimaro prepared to kill him, but the two were quickly separated by Gaara, who used his sand to knock them apart. Surprised by Gaara's sudden presence, Kimimaro tried to attack him with his Ten-Finger Drilling Bullets technique, which was blocked by the latter's Absolute Defense. Kimimaro saw Gaara as a stronger opponent than Lee, his sand being a strong defense. Recognizing Gaara as a long-range fighter and that it would be difficult to get close to him, Kimimaro continued using his Ten-Finger Drilling Bullets to attack while dodging Gaara's sand. Believing Gaara's use of sand was limited to his gourd sand, Kimimaro mocked him for being a careless fighter, but was caught and nearly crushed as Gaara pointed out his error, as he could always create more sand if he had his. Surviving by use of a bone shell under his flesh, Kimimaro emerged with his Sursed Seal of Earth aide, but his following statement of no longer underestimating Gaara was quickly disproven as the latter used a tsunami of sand to burry Kimimaro and again tried to crush him, using his Sand Waterfall Imperial Funeral technique. Overwhelmed, Kimimaro was forced to activate his Cursed Seal of Earth's second stage to break out. Though he managed to land a hit on Gaara, the latter's Armor of Sand completely protected him. Determined not to underestimate Gaara further, Kimimaro utilized his two-part Dance of the Clematis to kill him, but the latter countered with his Ultimately Hard Absolute Defense: Shield of Shukaku, which shattered Kimimaro's bone drill. After Gaara insulted his faith in Orochimaru, Kimimaro was burried two hundred meters below the ground. Kimimaro then used his Dance of the Seedling Fern to create a pointed bone forest out of the battlefield, which Gaara saved himself and Lee from, but allowed Kimimaro to emerge from one of the bones to attack him. However, Kimimaro died of his fatal disease in the middle of his final attack, just seconds before it could kill Gaara.
In part 2, Kimimaro was revived, alongside many more very powerful fighters, by Kabuto Yakushi as a military weapon for Akatsuki's side. In the war, he was teamed up with Hanzo of Amegakure and Chiyo of Sunagakure, and forced to go to the aide other revived shinobi, but ended up battling samurai reinforcements after they arrived, outmatching all whom he faced with his Shikotsumyaku kekkei genkai. After he had killed many, Kimimaro found himself confronted once again confronted by Naruto Uzumaki, who had become extremely more powerful, causing Kimimaro to state that he only needed to see him to know that time had truly passed, before dodging his Rasenshuriken attack. Kimimaro continued to do battle against the samurai until Kabuto cancelled the Impure World Reincarnation, seading Kimimaro's soul, along with all others revived by the technique besides Madara Uchiha, back into the afterlife.
Though he was born into the bloodthirsty Kaguya clan, of which he was the strongest member, as a child Kimimaro was never truly violent or murderous, and only fought because his clan needed him to, which was what he truly wanted. After his clan was wiped out, Kimimaro came to view Orochimaru, who took him under his wing, as a father figure(though the manga implied he thought of him as something more divine), becoming extremely loyal to him and very proud that he was chosen as Orochimaru's ideal vessel, which he came to view as his purpose. After he fell ill, losing this ability, Kimimaro cried over the loss of this viewed purpose. He also became enraged when Gaara insulted his faith in Orochimaru. Even after his revival, he still mantained this loyalty to his master. When he made friends, Kimimaro tended to be a thankful and loyal one, as he visited Jugo, who he recruited for Orochimaru, and thanked him for their friendship, before proceeding on his last mission. Like all his Sound Five teammates, Kimimaro was very disrespectful of his opponents, openly referring to them as trash, which he would attempt to clean up by killing them, even if they were his own allies, as he plotted to kill Tayuya, one of his teammates, after he saw her again following her failure to keep Naruto Uzumaki from following him. He did, however, have a sense of honor in battle, as he willingly paused his fight with Rock Lee to allow him to take his medicine when the latter asked. Kimimaro also had a bad habit of underestimating more powerful opponents, as he underestimated Rock Lee's Drunken Fist, which he could read or beat normally, and underestimated Gaara's sand powers and his Absolute Defense multiple times during their fight, resulting in him being overwhelmed for most of the fight and nearly killed multiple times.
Kimimaro was a very powerful and dangerous shinobi, easily the strongest his clan ever produced, and was the most powerful follower of Orochimaru. His power was such that he was able to easily defeat the Sound Four, all of whom were using their Cursed Seal's second stages, while using only his own's first, if not just part of it, forcing them to act under him as their leader. Even as a child, Kimimaro was a natural fighter, capable of easily defeating several experienced shinobi of Kirigakure the night his clan was killed. Kabuto noted that the killing of Hiruzen Sarutobi, the Third Hokage, would have been much easier if Kimimaro had not fallen ill.
Kimimaro's power mainly came from two things; his Shikotsumyaku, his clan's kekkei genkai, which out of his generation, only he had, and his Cursed Seal of Earth, one of Orochimaru's strongest Cursed Seals. Shikotsumyaku allowed him to use his skeletal structure as a weapon, manipulating his osteoblast and osteoclast cells to form new bones at will, shape them into weapons, and pull them from him body for personal use. He could also force the bones to emerge from his body to strike an enemy by surprise. Something esle about his bones was that they were as hard as solid steel which, if used defensively, allowed him to block very powerful attacks, such as Gaara's Sand Binding Coffin technique. Kimimaro's Shikotsumyaku made him very deadly at close-range combat, and he was noted by Rock Lee, a formidable Strong Fist expert, to be a taijutsu master, proven when he outmatched and nearly killed Lee. He mixed taijutsu together with Shikotsumyaku to create several deadly attacks, which he called "dances", which made him a very difficult opponent to most close-range fighters as, aside from his pre-mentioned outmatch of Rock Lee, he was also able to easily dispatch hundreds of shadow clones of Naruto Uzumaki, the Nine-Tails, Kurama's jinchuriki, all of whom had been enhanced by its chakra. Aside from this, Kimimaro had immense strength, speed, reflexes, stamina, and physical dexterity, and determination, able to easily evade Gaara's high-speed sand attacks, even in mid-air by changing position, pull himself, with aide from his Cursed Seal of Heaven's complete first stage, from Gaara's Sand Binding Coffin technique, and fight him, after having just fought both Rock Lee and Naruto immediately before, without a break, all this done while being in a dying state and unable to move his body of his own free will, having been forced to use pure will power to even pick himself up out of his bed.
His Cursed Seal of Earth greatly enhanced Kimimaro's Shikotsumyaku abilities and physical prowess in its first stage, and allowed him a transformation similar to a humanoid dinosaur in its second, which greatly increased his strength, to the point of smashing through Gaara's sand wall without trouble, at the cost of greatly hindering his speed. Using these two things together, Kimimaro was able to outmatch and nearly kill both Rock Lee and Naruto Uzumaki, and fight as a danger to the much more powerful Gaara, in the end overcoming his various sand techniques and nearly killing him, only to die in the middle of his last attack.