Sakon and Ukon

and his older brother were twin brothers from Otogakure and the apparent leader(s) of the Sound Four.

Personality
Sakon enjoyed bad-mouthing the opposition, and, like the rest of the Sound Five, he constantly referred his enemies as "trash". Orochimaru noted Sakon to be the fastest and strongest member of the Sound Four, traits Sakon was very proud of. When in battle Sakon liked to prolong the fight by toying with the opponent and use unnecessarily powerful techniques. This tendency of Sakon's caused him to slow down the rest of the group whenever he got interested in an opponent. Ukon was able to counteract this flaw by being more impatient and hasty than his brother, forcing Sakon to quickly end his battles. He and Ukon also both had their own perception of morality, like several other Sound Four members.

Appearance
Both Sakon and Ukon had dark grey hair with long bangs that covered each different eye their bangs were on opposite sides (Ukon's being on the left, Sakon's on the right). Each of the twins wore turquoise lipstick, and brown eye-liner, which made their appearance more feminine. They wore brown tunics with long black wristbands (which are mistaken for being part of their sleeves), black skin-tight shorts, and purple ropes tied around their waists. Sakon wore a dark-red, beaded necklace around his neck and a giant scroll behind his back. Both of the twins have a cursed seal planted on their foreheads which are covered by their bangs. At most appearances, Ukon is usually shown with a smirk on his face, and his head slightly tilted down. To further help distinguish between the two, Sakon wore beads around his neck and Ukon had a somewhat deeper voice.

Abilities
Sakon and Ukon were noted by Orochimaru, to be the strongest and fastest of the entire Sound Four, surpassed only by Kimimaro. Sakon tended to prove this point by unnecessarily using extremely powerful moves to show off. He was also proved to be quite proficient with fūinjutsu, as he performed the Four Black Fog Battle Formation with his comrades, and then the Dark Sealing Method by himself. When Ukon separated from his body, the two could perform Summoning: Rashōmon by standing at a certain distance away from each other.

Like the rest of the Sound Four, Sakon and Ukon had been given a cursed seal. When the second level of their seals were active, they resembled goblins with red skin, long white hair, and a single horn (on opposite sides for each brother's foreheads).

Kekkei Genkai
With their kekkei genkai, Sakon and Ukon were able to merge with the bodies of others. Ukon generally used this ability to remain within Sakon's body where he could bring out some of his body parts to aid Sakon in battle. In addition to defending Sakon's blind-spots, he allowed Sakon to perform three armed punches and three legged kicks. The two could heal quickly when merged together. Ukon could separate from Sakon's body so that the two can attack independently, though he was not used to moving on his own for too long and thus he would tire out easily.

With level 2 of their cursed seal, Sakon and Ukon could deconstruct their body on a molecular level and enter an opponent's body. At that point they were able to alter the cells and proteins of the target at will, effectively killing them, and then leaving the target to reconstruct their own body again. This technique, however, had the disadvantage of them taking the same damage as the body they had invaded, as seen when Kiba stabbed himself in the gut with a kunai causing Ukon to scream in pain and spit blood.

Invasion of Konoha Arc
Sakon and Ukon made their first appearance with the rest of the Sound Four, erecting a barrier to keep others from interfering in Orochimaru's fight with the Third Hokage. They later escorted Orochimaru when he fled.

Sasuke Retrieval Arc
The Sound Four escorts Sasuke Uchiha when he decides to join sides with Orochimaru. While resting along the way the Sasuke Retrieval Team caught up to them and the Sound Four are caught by Shikamaru's Shadow Imitation Technique, leaving them unable to move. Ukon however attacked Shikamaru and broke his hold. Jirōbō and Kidōmaru at different points stayed behind in an attempt to delay the Konoha ninja, but each time members of the Retrieval Team are able to catch up. On one such occasion, Sakon and Ukon were separated from Tayuya by Kiba Inuzuka and Akamaru when a paper bomb went off and knocked them all off a cliff. They then begin to fight Kiba and Akamaru and reached their second state after pounding them. Kiba and Akamaru then use the Human Beast Combination Transformation: Double-Headed Wolf technique to attack them seemingly ripping them apart until it is revealed that they had just split up. When Kiba and Akamaru attack again, Sakon and Ukon used their strongest defence Summoning: Rashōmon, to block them, but they dent it, impressing them. Sakon and Ukon then attacked, Akamaru however, takes the hit for Kiba and pees in Sakon's eyes, only this time made it an acid.

Ukon meanwhile used his ability to share a body to invade Kiba's body, while Sakon went and washed his eyes in the nearby river. After explaining what he was going to do, Kiba drew a kunai and stabbed himself in the stomach, guessing Ukon would feel it too. Ukon yells in pain, and before Kiba can kill them both, exits his body and tells him that he hadn't inflicted a fatal blow. Kiba then threw the Kunai at him and exploded some smoke bombs to allow him and Akamaru to escape, leaving a decoy to fool Ukon. When the smoke cleared, Ukon looked for him, but saw the decoy and approached it saying Kiba was pretty cold blooded. When he got too close, it exploded and sent several kunai at him impaling him several times. He then became angry that he fell for that trap and returned to Sakon to rejoin his body to heal, saying if he found them to keep them alive and he would kill them when he woke up. Sakon agrees saying they will kill them together.

After Sakon tracked them to where they jumped into the river, he found Kiba's jacket and gave it to Ukon, who had already woke up, to use it to sneak up on Kiba. When they found them, Ukon tried to kill them, but was stopped by Kankurō. Kankurō then engages Ukon, but is caught by Sakon, who came back when Ukon didn't return. Kankurō then revealed he had grabbed a puppet when he emerged from a pack on its back and impaled Sakon with several blades on the puppets arms. Ukon reached the second stage of his cursed seal and rushed over to shield Sakon from any further attacks. Sakon returned to his normal form and entered Ukon's body to heal. Ukon then commented that it's hard to move like that since he wasn't usually the one who was the main body. After Ukon insulted his puppet, Kankurō with both his puppets, Crow and Black Ant, engaged Ukon and trapped him in the Black Ant's belly, the very puppet he had insulted. Ukon then yelled and told him to let him out. Kankurō then prepared to kill him and Sakon. Ukon then shouted for him to let him out or he'd kill him. Kankurō then used his Black Secret Technique Machine One Shot to plunge several blades from Crow into specific places in the Black Ant's body, impaling Ukon and Sakon, killing them. Ukon's agonising scream could be heard from within the Black Ant, followed by his and Sakon's blood leaking out of the puppet.

Creation and Conception
Sakon was the final member of the Sound Four to be created by Masashi Kishimoto. After struggling to decide who Sakon should fight, Kishimoto decided to have Sakon take part in a two-on-two battle against Kiba and Akamaru. Thus he created Ukon and placed him within Sakon's body so that they could act as one person.

Video Games
Although Sakon is usually the default character in video games, some games allow the player to switch to Ukon, such as by pressing up on the d-pad.

Trivia

 * The first kanji in Sakon's name (左) means "left", while the one in Ukon's name (右) means "right".
 * Sakon can be seen in the omake of Naruto Shippūden episode 129 with Kidōmaru, picking masks.
 * Sakon's hair is shown as dark blue in the manga. In the anime it has a light bluish-grey colour.
 * According to the Naruto Official Databook:
 * Sakon's favourite phrase is: "The first and only".
 * Ukon's favourite phrase is: "The older brother up the younger brother".
 * Sakon and Ukon had completed 46 official missions in total: 20 D-rank, 15 C-rank, 8 B-rank, 2 A-rank, 1 S-rank.