Sound Four

The was an Otogakure team that served as Orochimaru's elite bodyguards. Despite the name, there are technically five members because Sakon and Ukon share positions.

History
In the anime, the Sound Four were originally prisoners of Orochimaru, forced to fight other prisoners to the death in battle royales. By surviving their respective matches, they proved themselves to be the strongest of Orochimaru's prisoners and as such were made his bodyguards. The Sound Four were at some point forced to accept Kimimaro as their leader, who easily defeated them all in battle and, because of his Shikotsumyaku abilities, was slated to be Orochimaru's next host body. Under Kimimaro their group was known as the.

In the anime, the Sound Five assisted Orochimaru with assassinating the Fourth Kazekage and killing Shiore's team during the Chūnin Exams in Konohagakure. Kimimaro fell terminally ill after this, forcing him to withdraw from the group; he became ill at some unspecified time in the manga. Now the Sound Four once again, they stayed by his side by impersonating the Kazekage's bodyguards while Orochimaru himself impersonated the Kazekage. When Orochimaru initiates the Konoha Crush during the third phase of the Chūnin Exams, the Sound Four erect a barrier around the site of his battle with the Third Hokage so that nobody can interfere. When Orochimaru's arms are sealed by the Hokage, the Sound Four help him return to Otogakure.

To escape the damage to his arms, Orochimaru needs a new body, a role he selects Sasuke Uchiha for. He sends the Sound Four back to Konoha to recruit Sasuke, which they accomplish by demonstrating how significantly stronger Orochimaru's cursed seals make them. Sasuke agrees and, on Orochimaru's instructions, he is appointed the Sound Four's new leader as they escort him back to Oto. Once sufficiently far from the village, the Sound Four give Sasuke a Mind Awakening Pill to forcefully mature his cursed seal and start carrying him while his body undergoes its changes. They encounter the Konoha Special Mission Platoon along the way and are forced to use their cursed seals to defeat them.

While recovering from their previous fight, the Sound Four are found by the Sasuke Recovery Team. From trying to delay the Recovery Team, the Sound Four gradually lose members: first Jirōbō to Chōji Akimichi and then Kidōmaru to Neji Hyūga. Taking so long when Orochimaru desperately needs Sasuke's body compels the dying Kimimaro to go after the Sound Four. He locates them in time to reclaim Sasuke from Naruto Uzumaki, and threatens to personally kill Tayuya and Sakon and Ukon if they don't deal with the Recovery Team. Tayuya and Sakon and Ukon nearly succeed against their respective opponents, Shikamaru Nara and Kiba Inuzuka, but they are stopped and killed by the Sand Siblings, Temari and Kankurō. Kimimaro himself succumbs to his illness while fighting the third sibling, Gaara, but their mission is partially successful: Sasuke reaches Orochimaru, though it's too late for him to be a host body.

In the anime, the Sound Four are reincarnated three years later by Kabuto Yakushi to fight for Akatsuki during the Fourth Shinobi World War. Kabuto tells them he is helping Orochimaru grant them a wish by allowing them to take vengeance against those who killed them. The Sound Four seek out and engage the members of the Recovery Team they fought before they died. Although they are unable to compete with the now-stronger Recovery Team, the Sound Four are able to trap them all with the Space–Time Technique Formula: Underworld Turnover, which promises to kill them all given enough time. Shikamaru tricks the Sound Four into amplifying their hatred, attracting Naruto to their location and allowing him to release the Recovery Team, defeat the Sound Four, and send their souls back to the Pure Land.

Kabuto assimilates samples of the Sound Five's DNA into his body, allowing him to freely manifest each of them so that he can use their abilities.

Abilities
The Sound Four are among Orochimaru's strongest underlings. They are well-versed in various barrier ninjutsu and fūinjutsu, though those they are seen using require all four of them to participate. In the anime, they each also have their own type of summon, which they call upon for the Four Beasts Encirclement Formation. Their role as Orochimaru's bodyguards makes them overconfident in their abilities, tending to cause them to waste time: 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 likes to show off by using flashy jutsu; Tayuya has a "doesn't-want-to-lose" mentality. Despite their different temperaments and varying styles of combat, their team balances out well.

To help them protect him, Orochimaru gave each member of the Sound Five a cursed seal, which greatly enhances their individual abilities. In the anime, Shikamaru states that each members' prowess was jōnin-level.

Missions
During the Konoha Crush, the Sound Four erected a barrier which prevented anyone from meddling in the battle between Orochimaru and The Third Hokage, Hiruzen Sarutobi. Although Orochimaru succeeded in killing Hiruzen, his arms were crippled with necrosis, thus halting the Konoha Crush. The Sound Four 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 Four, 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 Raidō Namiashi. Soon after, Konoha's Sasuke Recovery 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: Unknown
 * Status: Partial Success

Kimimaro was brought back as one of the many powerful soldiers to participate in the Fourth Shinobi World War. In the anime, Kabuto also reincarnated the other members of the Sound Four for dual purposes: to test out how a Cursed Seal would function in reincarnated shinobi and to stall for time while he prepares his trump card. The four, unaware of this, believed they were brought back by Orochimaru as a reward for their loyalty, and a chance to avenge their own deaths upon the team who defeated them. Though they were ultimately defeated by Naruto and failed to get their revenge, they succeeded in showing Kabuto his experimental results and gave him the time needed.
 * Stalling for Time
 * Rank: Unknown
 * Status: Success

Trivia

 * The symbol on the Sound Four's tunics is the yin-yang, though the yin colour (black) is missing. The missing yin represents imbalance, preventing harmony in life.
 * Each member of the Sound Four has a cardinal direction associated with them, a position they tend to take when performing group jutsu: Jirōbō of the South, Kidōmaru of the East, Sakon of the West, and Tayuya of the North.