Little is known of Kidomaru's background, other than that he was chosen by Orochimaru to be one of his bodyguards, the Sound Four, being teamed up with Sakon and Ukon, Tayuya, and Jirobo. Later, they were defeated by Kimimaro, who forced them to accept him as their leader.
Kidomaru made his debut in the series at the Chunnin Exams finals battle arena, alongside his fellow Sound Four members erecting a barrier for his master, Orochimaru, to fight the Third Hokage, Hiruzen Sarutobi within. After Anbu arrived as backup, the Sound Four erect a barrier on the inside to protect themselves from Hiruzen. After Orochimaru's arms were crippled, by his order, Kidomaru and his teammates undid their barriers and carried him away after the mission to destroy Konohagakure failed. Much later, after Orochimaru failed to get healed by Tsunade, he sent Kidomaru and the other Sound Four members to Konohagakure after Sasuke Uchiha, with them managing to convince him to return with them with offers of power from their master and accepting him as their new leader. After putting Sasuke in a death-like state so that his Cursed Seal could mature to another level, Kidomaru and the others used their sealing powers to coffin him to preserve his life during the process, and carried him on. Along the way, they encountered Genma and Raido, a pair of Jonin from Konohagakure, who they managed to defeat. While resting up from their fight, the Sasuke Retrieval Squad found them, but Jirobo, one of Kidomaru's teammates, trapped them and volunteered to kill them. He failed, however, and after Shikamaru Nara, desguised as Jirobo, approached them, Kidomaru and the other recognized him as an imposter by his manner and Kidomaru tossed Sasuke's coffin to Tayuya, and one by one caught all four of the remaining retrieval shinobi in his webbing. Attempting to kill Naruto Uzumaki first, Kidomaru found that the real one had not been caught and countered his attack. Before he could defeat Naruto, Neji Hyuga stepped in and countered him, having freed the others. After they left, Kidomaru then found himself forced to battle and defeat Neji, before he could follow his teammates.
Kidomaru found that close combat was not the way to battle Neji after the latter nearly killed him with his Gentle Fist style, which he countered by growing his unique, bodily metal on his flesh to shield the chakra from Neji's hands. Attempting to attack him from behind with silent, single attacks by way of kunai failed as well thanks to Neji's Byakugan, which also countered a more large-scale attack. Realizing and surprised by the power of Neji's eyes, Kidomaru activated the complete first stage of his Cursed Seal and began to take the battle seriously. He summoned his Kyodaigumo summon, a giant spider, just like its name suggests, and had it blanket Neji in webbing with its Rain of Spiders technique, allowing him to prevent Neji's Eight Trigrams Palms Revolving Heaven technique from being used correctly so that he could kill him, but Neji was still able to block his attack and continued to counter the Rain of Spiders by use of his Eight Trigrams: Sixty-Four Palms, and then later, his doubled version, One-Hundred Twenty Palms, which Kidomaru noted would kill him if it hit him. Continuing to attack him, Kidomaru eventually landed a hit on him, which revealed that Neji's Byakugan had a blind spot, which he struck again more directly to confirm. Continuing to use his techniques together more specifically, Kidomaru managed to strike Neji twice more, causing him to fall. Signalling the Kyodaigumo to finish Neji, the latter counters, only for Kidomaru to stab three more kunai into him after the giant spider transformed into webbing. Believing he had won, Kidomaru started to leave, becoming surprised and delighted when Neji stood up again. Activating the second stage of his Cursed Seal, Kidomaru created his Spider War Bow and tried to shoot Neji's blind spot fatally, but it was diverted by a chakra barrier, striking him through the shoulder instead.
Surprised, Kidomaru produced another arrow with a thread attached to ensure he would hit Neji fatally as he ran, but it was diverted by a tree. Leaping to the top of the treeline for a better advantage point, Kidomaru produced a new arrow capable of slicing through a tree should it hit one and again with a thread attached so he could guide it to his target. While this time was a success, and Kidomaru shot Neji through his abdomen, the latter sent a burst of chakra back up the line to him, damaging several of his internal organs. As he fell, Kidomaru cut the thread and prepared to leave, unaware that Neji was appraoching him as he believed this to have been the latter's dying effort. He soon found himself face to face with Neji, who jumped up and struck him with a full on attack from his Eight Trigrams: Sixty-Four Palms, turning off his chakra and dealing a fatal blow to Kidomaru's heart. As he reverted back to his original form, Kidomaru questioned how Neji lived and, though he stated that chasing Sasuke was useless, Neji said that Naruto could save him from the dark path he chose. Coughing blood, Kidomaru cursed Neji as he died.
In part 2 in the anime, Kidomaru and his teammates were revived by Kabuto Yakushi, and they confronted their opponents again. Kidomaru fought Neji, but lost, despite being stronger under Kabuto's Summoning: Impure World Reincarnation, and activated the Space-Time Technique Formula: Underworld Turnover technique to transport himself and his teammates, as well as the first opponents of their last battle into a kind of barrier where they could fight them again. Kidomaru and his comrades switched around some, and he later told the Konohagakure shinobi present that even if they defeat him and the others, they will not get free. With the hate they feel for their opponents increasing their power, Kidomaru and the other Sound Four overwhelm their opponents, causing Shikamaru to bait their hate further, which eventually summoned Naruto Uzumaki, who freed them. Kidomaru and the others tried to kill him instead, but were defeated and sent back into the afterlife by Naruto as the barrier dissolved.
Kidomaru loved fighting and typically saw it as playtime, in which he would use standard gaming language to specify the level of an opponent. Like all the Sound Four(Five counting Kimimaro), Kidomaru was very arrogant towards his opponents and often called them trash. He was also the only member of the Sound Four not to have a view of morality.
Kidomaru was a very powerful shinobi, despite his young age, strong enough to become one of Orochimaru's Sound Four bodyguards. Kidomaru was able to easily catch multiple Anbu off-guard and repel them during Orochimaru's flee of Konohagakure and was also able to, alongside his teammates, defeat Genma and Raido, two Jonin of Konohagakure. He was also able to easily outmatch a whole group of Konohagakure Genin, trapping three in single attempts. Kidomaru was also able to fight superiorly to Neji Hyuga, a natural genius of the Hyuga clan and one of their most powerful Byakugan users, nearly killing him in a fight that almost stalemated.
Made more obvious in the anime, Kidomaru was very skilled in taijutsu, being noted by Shikamaru Nara to be Jonin-level in that way. He had six arms, unlike anyone else, which allowed him to fight and strike opponents more easily, perform multiple hand seals at once, and attack multiple targets at long range. He also had a third eye on his forehead, which he usually kept covered, which gave him unusual precision and allowed him to detail more accurately at a distance. Like most of Orochimaru's stronger servants, Kidomaru was branded with a Cursed Seal. In its first stage, his physical might became enhanced tremendously, as did his ninjutsu. Kidomaru could spin webs by mixing his chakra with spit or sweat, allowing him to trap opponents in webbing so strong, only Neji Hyuga's Gentle Fist has ever been known to penetrate it. He could also produce a type of metal called Sticky Gold from his mouth and sweat glands that was impervious to chakra, which allowed him to both block physical attacks, even the Gentle Fist, and kill his opponents quite quickly. Kidomaru was able to create a bow from this metal, called the Spider War Bow, whose arrows could easily smash trees and create craters. He only used this technique when in his second stage transformation, in which he basically resembled a humainoid spider, capable of spinning webs without using chakra. Kidomaru was also very analytical, capable of easily locating his opponents weak point and exploiting it, shown most notably when he fought Neji Hyuga, finding the blind spot of his Byukugan easily, something which impressed Neji enough to acknowledge Kidomaru as his strongest opponent.