Sound Four

The were Orochimaru's elite bodyguards, though they are technically five despite Sakon and Ukon counting as one entity because of their kekkei genkai.

Overview
Seeing their opponents as inferior to themselves, each member was given a cursed seal. The four were reluctantly forced to accept Kimimaro in their ranks when he single handily defeated them all, their group temporarily called the until Kimimaro's illness kept him from participating normally as the Sound Four supported Orochimaru during the Invasion of Konoha.

History
Despite their young age, all members of the Sound Four were among Orochimaru's strongest ninja and become his personal bodyguards. In the anime, they were originally Orochimaru's captured experiment subjects, and after being pitted against other prisoners in a death brawl and surviving via desire to live, they were granted the positions of Orochimaru's bodyguards.

The strongest among them was Kimimaro, who was one of Orochimaru's most prized subordinate, possessing the rare kekkei genkai Shikotsumyaku of the Kaguya Clan and a candidate to be one a host body for their master. After a young Kimimaro befriended Jūgo and brought him to Orochimaru, the Sannin learned of senjutsu and master it at Ryūchi Cave. Unable to use Sage Mode properly, Orochimaru instead devised the cursed seals by combining his senjutsu chakra into the mutative enzymes he isolated from Jūgo's blood. After testing his juinjutsu on several subjects, Orochimaru placed the finalised versions on the Sound Four to increased their strength.

Sometime later, Kimimaro was branded with one of Orochimaru's strongest cursed seals, the Cursed Seal of Earth, and then fought the Sound Four to test his new powers. After defeating the Sound Four with ease and leaving a rather fearful and negative impression on them, Kimimaro become the group's leader before stepping down due to his terminal illness.

Chūnin Exam Arc
In the anime, Kimimaro and Sound Four was revealed to have participated in for killing the Kusagakure ninja Shiore and his team so that Orochimaru could impersonate him. After assassinating of the Fourth Kazekage and his bodyguards, Orochimaru and the Sound Four masqueraded as them in perpetration to invade Konohagakure, whilst Kimimaro's disease fully manifests and was send back to Otogakure to be (unsuccessfully) treated by Kabuto Yakushi.

Konoha Crush
Once the invasion of Konoha began, the Sound Four discarded their disguises alongside their master and erected the Four Violet Flames Formation barrier to prevented anyone from interfering in the battle between Orochimaru and The Third Hokage, Hiruzen Sarutobi. After his defeat, they carried Orochimaru out of the village and retreated back to Otogakure.

Sasuke Recovery Mission
When Orochimaru sent the Sound Four to bring him Sasuke Uchiha, they are soon confronted and entered multiple battles within the three-day limited time of their mission. After exerting themselves against two Konoha Jonin, Jirōbō and Kidōmaru were respectively killed by Chōji Akimichi and Neji Hyūga when they and their team were deployed to bring Sasuke back to Konoha. Sakon and his brother overwhelmed Kiba Inuzuka while Tayuya almost killed Shikamaru before the remaining Oto ninja were killed off when their opponents received aid from Kankurō and Temari. Though Kimimaro later joined the fray to ensure the mission succeeds (which did, as without him the opposing team would have retrieved Sasuke) he died from his illness as he almost killed Rock Lee and Gaara.

Fourth Shinobi World War: Climax
It would be revealed years later during the Fourth Shinobi World War that Kabuto Yakushi assimilated DNA samples from the Sound Four and Kimimaro, using Sakon and Ukon's Attack of the Twin Demons ability to create a shape-shifting construct from his body to use the abilities of the entire Sound Five. Kimimaro himself was brought to life with Summoning: Impure World Reincarnation to assisted in the war, believing Orochimaru was the one who summoned him, and fought diligently until his soul was released back to the afterlife.

In the anime, the Sound Four are reincarnated by Kabuto as a part of a "wish granted" by Orochimaru, from a promise that they would become "the ones who seek vengeance" after their deaths. Kabuto took advantage of this not only for them to serve as test subjects on how the cursed seals function with reincarnated ninja, but also as a diversion to slow down the remaining Allied Shinobi Forces while he prepared his trump card. Believing they were all brought back by Orochimaru as a reward, the Sound Four engaged their respective Sasuke Retrieval Team opponents in battle again. Though their opponents got stronger since the last time they fought, the Sound Four trapped them with the Space–Time Technique Formula: Underworld Turnover technique so they can have their revenge even if they are somehow defeated. However, Shikamaru tricks the Sound Four into embracing their undying hatred so Naruto can find the barrier and destroy it. Denied their revenge, the Sound Four attack Naruto before he easily defeats them as they are sent back to the afterlife.

Abilities
Despite being young, all four of them are strong enough to become Orochimaru's bodyguards, and were all talented with barrier and sealing techniques, as well being knowledgeable of Juinjutsu and Orochimaru's curses seals. The group also excelled at Cooperation Ninjutsu and can preformed many high-level, advanced techniques when working together. Shortly after their introduction during the invasion of Konoha, they used Four Violet Flames Formation to create a box-like barrier, that causes anything that touches it to burst into flames. When the group later fetched Sasuke, they used the Four Black Fogs Formation and Dark Sealing Method to protect Sasuke from harm. As the group later rested, they set up a Barrier Method Formation as well as several traps around a large part of the forest. In the anime, they were also capable of using the Space–Time Technique Formula: Underworld Turnover.

Each member of the Sound Four also had a cardinal direction associated with them; this was probably a reference to their positions when performing techniques as a group: Jirōbō of the South, Kidōmaru of the East, Sakon and Ukon of the West, and Tayuya of the North.

As with most of his powerful followers, Orochimaru branded them with different cursed seals, which greatly enhanced their individual abilities. In the anime, Shikamaru stated that each members' prowess was of jōnin-level. Their individual abilities made them a well-balanced team overall:


 * Jirōbō possessed brute strength and powerful Earth Release techniques, particularly his Earth Release Barrier: Earth Prison Dome of Magnificent Nothingness, can slow and weaken enemies by stealing their chakra.
 * With his unique spider-like abilities, Kidōmaru was talented in long-range attacks, surveillance and detection.
 * With their kekkei genkai, Sakon and Ukon were skilled at close-range and combination attacks.
 * Tayuya was capable of multi-directional support through genjutsu or by controlling her Doki.

Missions
During the Invasion of Konoha, the Sound Four erected a barrier which prevented anyone from meddling in the battle between Orochimaru and The Third Hokage, Hiruzen Sarutobi. After his defeat, they carried Orochimaru out of the village and to safety. It was later noted by Kabuto that had Kimimaro not fell ill and stepped down from the Sound Five, this mission would have gone much smoother, something Orochimaru agreed with.
 * Guard Orochimaru
 * Rank: Unknown
 * Status: Partial Success

On Orochimaru's orders, the Sound Four convinced Sasuke to joined them after showcasing their power and escort him to Orochimaru so he could use the Living Corpse Reincarnation on Sasuke to make him his new host body. They were given about a three-day time limit to complete this mission, however, the Sound Four soon engaged in an exhausting battle with Genma Shiranui and Raido Namiashi. Soon after, Konoha's Sasuke Retrieval Team confronted them, forcing both teams to split up one by one in order carry out their mission. Although they failed to bring Sasuke within the time limit for their master to use as a host, the Sound Four was able to stop Konoha's forces and their allies from reaching him with help from the powerful, yet terminally-ill Kimimaro. At the cost of all the members' lives, Sasuke successfully made it to Otogakure to begin his training with Orochimaru.
 * Escorting Sasuke
 * Rank: Unkown
 * Status: Partial Success

Other Media

 * The Sound Five are playable characters in Naruto: Gekitō Ninja Taisen! 4, but they only appear with the Second Stage of the Cursed Seal.
 * The Sound Five are playable in Naruto: Ultimate Ninja 3, Naruto Shippūden: Ultimate Ninja 4, and Naruto Shippūden: Ultimate Ninja 5 with both their normal and cursed seal forms.
 * The Sound Four are support-only characters in Naruto: Ultimate Ninja 2, Naruto: Ultimate Ninja Storm, Naruto Shippūden: Ultimate Ninja Storm Generations, and Naruto Shippūden: Ultimate Ninja Storm Revolution, but only appearing in their normal forms.
 * The Sound Five also appeared in Naruto: Ninja Council 2 European Version, Naruto: Ninja Council 3 and Naruto: The Broken Bond.
 * The Sound Five made cameos appearances in Finally a clash! Jōnin vs. Genin!! Indiscriminate Grand Melee Tournament Meeting!! OVA, Hidden Leaf Village Grand Sports Festival! OVA, Naruto x UT OVA, the omake of Naruto: Shippūden episode 129, and episode 31 of the anime adaption of Rock Lee no Seishun Full-Power Ninden.

Trivia

 * The recurring symbol on the Sound Four's tunics was the yin-yang, though the yin colour (black) was missing. The missing yin represented imbalance, alluding to their evil natures and to that of the seals, preventing harmony in life.
 * Jirōbō and Sakon (and Ukon) specialised in close-quarter combat, while Kidōmaru and Tayuya specialised in long range combat. Kimimaro was balanced in both types.
 * Each member of the Sound Four tended to have a flaw in their personality that slows down the team: Jirōbō gets hungry and stays behind to feed, Kidōmaru tends to play around with his opponents if they interest him, Sakon can easily lose his temper and showcases the fact that he is the strongest of the four by not stopping until his opponents are dead, and Tayuya has a "doesn't want-to-lose" mentality.
 * In the anime during a flashback, it was shown that the Sound Four obtained the second stage of their cursed seals after the Invasion of Konoha.