Jūgo

, was being held at Orochimaru's North Base, which was also where most of Orochimaru's secret research was conducted. He was recruited as a member of Taka.

Background
Jūgo's personality is usually quiet and unassuming, but, when angered, those around him stand little chance of survival. One time, he even became so angry that he devoured an entire village. This has caused others to label him as the "Scales", where anything could tip the balance. Cursing his existence, he took to secluding himself in caves, hoping to bring no-one any harm. This lasted until Kimimaro came to him, who was himself the last remnant of his own Kaguya clan. Following Kimimaro, Jūgo allowed himself to be one of Orochimaru's test subjects. Upon examination, Orochimaru was able to isolate enzymes in Jūgo's blood that caused him to transform. By extracting these enzymes, Orochimaru was able to use them to produce similar, but more controlled, effects in other people, leading to the creation of the cursed seal. As time passed, Kimimaro died, then Orochimaru followed him, and Jūgo shut himself away once more.

Appearance
Jūgo has a bracket-shaped symbol on both of his palms. Whether or not this has any significance has yet to be seen. He is the tallest, non-animal character in the series who's precise height (202 cm) is known. Jūgo wears a black shirt, tan pants, and a blue cloak. After Taka had allied with Akatsuki, Jūgo was shown wearing an Akatsuki robe.

Jūgo has spiky orange hair, and an usually calm face. However, when affected by his murderous side, his skin turns dark, and he grows various weapons and appendages to suit his battle combat situation, as well as having a deranged look.

Personality
While Jūgo initially appeared quite bloodthirsty, Karin noted that this was only common behavior when he was enraged; Jūgo himself didn't want to kill anyone. Jūgo's fits of rage are random, and thus, the reason why he willingly remains confined. The only reason he agreed to go with Sasuke is because he views Sasuke as the only person capable of preventing him from killing people while enraged, by the means of killer intent or the Sharingan. Before Sasuke, it was Kimimaro who kept Jūgo in check, and as Kimimaro was the only person Jūgo came into any contact with, the two grew close. After hearing that Kimimaro sacrificed his life to deliver Sasuke to Orochimaru, Jūgo believes that Kimimaro's spirit continues to live on in Sasuke.

Suigetsu can't stand Jūgo, and commented that one of the reasons he had to retrieve the Decapitating Carving Knife was because of him. Karin noted that Jūgo is mentally unstable, a view confirmed when Jūgo was muttering to himself over who he would kill next, which he would determine by gender. While discussing Sasuke Uchiha's team with the other members of Akatsuki, Pain referred to Jūgo as, referencing his dual personality. The English manga used the term "Bipolar Jūgo", obtaining the same effect.

Hunt for Itachi arc
After defeating Orochimaru, and recruiting Suigetsu and Karin, Sasuke Uchiha travelled to Orochimaru's North Base, to recruit Jūgo. Initially unwilling to join forces with Sasuke, Jūgo tapped into his Cursed Seal, but was then frightened into releasing it by Sasuke's killer intent. He then joined the newly formed Hebi in their mission to hunt down and kill Akatsuki's Itachi Uchiha, Sasuke's older brother.

Jūgo would later discover multiple hidden bases belonging to the Akatsuki, where Sasuke confronted a clone of Itachi in one of them, who challenged Sasuke to meet him at the Uchiha Clan Stronghold. Jūgo remained behind with the other members of Hebi and Kisame Hoshigaki as Sasuke confronted Itachi.

Hunt for the Eight-Tails arc
After Itachi's death, and Sasuke's "education" in his brother's true past by Madara Uchiha, Jūgo and the other members of Hebi were reformed into Taka. Having allied themselves with the Akatsuki, Taka was sent to capture the Eight-Tailed Beast, so that it could be extracted from its host, Killer Bee. Infiltrating Kumogakure, they confronted Killer Bee, only to have him defeat Suigetsu. When Jūgo attempted to defeat him as well, Killer Bee overpowered him using the sword Suigetsu had wielded, which originally belonged to Zabuza Momochi.

After Sasuke was critically injured, Jūgo tells Karin that she did not have enough chakra to heal him and starts to infuse some of his flesh with Sasuke, to heal his wounds, saying it would work as he was compatible for his cursed seal. This however somehow reduced him to a younger appearance. When their team started working together, Jūgo concentrated on removing his teammates from danger, even though he initially objected to rescuing Karin, as he thought she would die from Sasuke's Amaterasu.

Sasuke was eventually able to capture Killer Bee, albeit a fake, and Jūgo recuperated with the rest of Taka. As Taka rested in one of Akatsuki's hideouts, Karin sensed a spy had followed them. Jūgo and Sasuke went and intercepted him, and left the hideout for a new one shortly after.

Five Kage Summit arc
Taka later set out for Konoha. On their way they were intercepted by Tobi who informed them that Konoha had already been destroyed. Zetsu, who suddenly appeared, then explained that a man named Danzō had been named Hokage. As per Tobi's advice and orders, Sasuke changes their goal to the Kage Summit. Taka is then guided by Zetsu, who had split up into two bodies.

Jūgo and the rest of Taka arrived at the Land of Iron, and after Suigetsu scouted the area and reported there are many guards, Sasuke tells Jūgo to use animals to find the least guarded route. Their presence is soon discovered and Sasuke engages the samurai that come after them. When Karin becomes preoccupied worrying about Sasuke, Jūgo tells her to continue looking for Danzō while he goes to help Sasuke.

Taka is attacked by Kumogakure ninja that Jūgo identifies as two jōnin and the Fourth Raikage. Knowing their presence will make it difficult for Karin to locate Danzō without exposing herself, Jūgo resolves to killing them. He transforms into his Curse Seal level 2 and goes into his murderous mental state. The Raikage quickly overwhelms him and forces into the wall, punching through a defensive shield on his arm and into his chest. Though he has seemingly been killed, Jūgo smirks and aims dozens of boosters from his back straight at the Raikage, firing them at point-blank range. Believing the Raikage to be dead, Jūgo prepares to attack someone else, but he is then hit again by the Raikage with a sudden elbow strike. Jūgo smashes against the wall and seems to be knocked unconscious.

As the battle unfolds, Sasuke destroys the room they are in and Jūgo, having regained consciousness, is buried in rubble. He absorbs the body of a nearby samurai, healing his wounds and returning him to an adult state. He is later seen with Suigetsu, who suggests that they should follow the Raikage and Sasuke. Jūgo tells him not to do so because they would be killed. However, Suigetsu says that he has a plan in mind. They try dressing up as samurai to flee the area, but are quickly caught.

Cursed Seal
Jūgo is the very origin of the Orochimaru's Cursed Seals, so he is able to use its powers to its full extent without it eroding his body. Also, unlike the cursed seals distributed to other people, Jūgo can have many more forms to change to, as opposed to being restricted into one. He also refers to people with a Curse Seal as a copy of him.

His brief fight with Sasuke and Suigetsu revealed that Jūgo can control his transformation, unlike the static effects of a standard Cursed Seal. When battling Sasuke, he changed his left arm into a piston-like ram to increase his punching power, and then altered it into a massive axe blade to counter Suigetsu's sword. He is also capable of doing only a partial transformation, invoking a level two form over one portion of his body without completely changing.

Jūgo's calmer personality is able to throw people by using his arm and releasing chakra out the other direction. This can also be used for escaping, charging right out of the battle with great speed.

He can also fuse part of his body, while in Cursed Seal form, to replace parts of other Cursed Seal-infected people's bodies, as he does to Sasuke. However, the downside to this appears to be it reverts Jūgo to the appearance of a child. He can also take bodies of others to fuse into his own body to repair injuries.

By entering into his Level 2 state, Jūgo gains massive power boost, but loses his mind into his murderous side. As with all others with a Cursed Seal, Jūgo's skin turns dark, with black sclera in the eyes. His elbows have sharper edgings, his nails sharpen, he grows horns at the top of his head that extends to his cheeks, and on his back are what appears to be six jet boosters like appendages, similar to the bones on the back produced by Kimimaro in his Level 2 form, that release fire. These appendages can increase in number and extend forward to aim at a target of Jūgo's choosing, then launch massive blasts of chakra with cannon-like force, devastating an opponent, especially at point-blank range. In his Level 2 form, Jūgo is also very resilient, as he took a punch from the Raikage right through the arm and chest and managed to retaliate with ease.

Communications with Animals
Jūgo is able to understand and communicate with animals, such as birds, and is able to request them to help him accomplish tasks, such as acting as scouts.

Trivia

 * Jūgo will be a playable character in Naruto Shippūden: Narutimate Accel 3 and Naruto Shippūden: Ryujinki.