Kakuzu

was the partner of Hidan despite their mutual dislike of each other. Kisame laughingly referred to Hidan and Kakuzu as the "Zombie Brothers".

Background
When still loyal to Takigakure, Kakuzu took on a mission to assassinate the First Hokage. This mission, however, ended in failure before the might of the First Hokage's Mokuton jutsu. Despite the insurmountable danger faced in the mission, what awaited his return to his village was the stigma and harsh punishment associated with failure of his objective. In response to this treatment, a wrong levied against a shinobi who had put life and limb on the line for his village, Kakuzu came to hold a violent hatred to his village as he escaped from imprisonment. In his flight from the village, Kakuzu killed the village elders, took their hearts, and fled with knowledge of the village's most prized forbidden techniques. Eventually he joined Akatsuki and was given a number of partners, most of whom he killed. Pain states that his reason for joining Akatsuki is "Resources".

Personality
Kakuzu was a greedy, miserly individual, arranging goals in terms of the highest profit he could gain from them, and was often unwilling to involve himself in something unless there are something to gain. He even remarked that money is the only dependable thing in the world. Due to this end, he referred to himself as the "Treasurer of Akatsuki". Given his friendly relationship with Genji, his bounty officer, it would seem he collected bounties rather frequently to earn cash, and did so (or at least tried) during his missions on several occasions. The frequent side tasks and devotion to money were both major points of contention between Hidan and Kakuzu. He also seemed to respect an opponent who thinks, as shown with his reaction to Kakashi's counters to Kakuzu's masks and Shikamaru's quick analysis of Hidan's curse, and even mentioning Shikamaru would have been a good bounty in the future.

Out of all the Akatsuki members, Hidan and Kakuzu displayed the most animosity towards each other, since neither of them were very fond of each other's interests. The two often traded barbs with one another, Kakuzu's usually having better timing than Hidan's. Hidan has shown great annoyance with Kakuzu's greed and occasional habit of doing or saying blasphemous things, such as attacking a temple and killing the head monk for the bounty on the monk's head. Kakuzu, in turn, disliked Hidan's religion, believing the rituals associated with it to be a waste of time. Kakuzu was also rather impatient with Hidan's drawn-out speeches and battle style.

The only reason that Kakuzu put up with Hidan was because he can't get rid of him. Due to his violent temper, Kakuzu often killed anyone close by when enraged. Hidan, therefore, is the perfect partner for Kakuzu, because of Hidan's apparent inability to die. Kakuzu's somewhat indiscriminate attack style also make Hidan an ideal partner, since Kakuzu doesn't need to worry about catching his partner in the crossfire.

Despite his obsessive personality and violent rage, Kakuzu was much more cautious than his partner and was not as arrogant, never mindlessly rushing into battle like Hidan. Kakuzu frequently warned Hidan not to let his guard down, and then teased Hidan when he inevitably did. Kakuzu apparently seemed quite willing to follow orders. When ordered to retreat by the Akatsuki leader, Kakuzu complied immediately (while Hidan attempted to argue), despite the rather large bounty he could have received by taking Asuma. He seemed to forget the greater goals of the organization when enraged, as he attempted to kill Naruto in spite of Akatsuki's need to capture all the tailed beasts alive.

Hidan and Kakuzu arc
Kakuzu first appeared with his partner, Hidan, in their pursuit of the Two-Tailed Demon Cat's host, Yugito Nii, who reveals she allowed herself to be cornered in order to spring a trap on them and eliminate them herself. Yugito then transformed into her full demon form, a large flaming cat, but the Akatsuki duo still managed to defeat her and gave her body to Zetsu before they continued to the Land of Fire.

On their way, Kakuzu decided to attack the Fire Temple in order to collect the bounty on the head monk, Chiriku, who was listed in the bingo book with a thirty million ryō bounty. They slaughtered most of the other monks during the event, but one escaped to warn Konoha of the incoming threat.

Upon getting the notice, Tsunade assigned the Niju Shotai to track down and eliminate Kakuzu and Hidan. Meanwhile, Kakuzu took Chiriku's body to a bounty station hidden in a bathroom, while Hidan chose to wait outside. When Kakuzu finally left the bathroom after counting the money, he found a Niju Shotai team, led by Asuma Sarutobi, attacking Hidan. He attacked Shikamaru Nara in order to free Hidan, but was forbidden from further participation in the battle by the overconfident Hidan himself. Kakuzu complied, but insisted that he will get to have the thirty-five million ryō head of Asuma afterwards. In the ensuing battle, Hidan managed to ingest Asuma's blood to start his curse jutsu ceremony on him, but Shikamaru was able to stop him with his Shadow Possession Technique. When Asuma managed to decapitate Hidan, Kakuzu finally intervened and reattached Hidan's head back to his neck using the threads in his body. Kakuzu then fought with Kotetsu and Izumo, easily holding the two off, while Hidan dealt a fatal blow to Asuma. Their battle was interrupted by the appearance of another Niju Shotai team, but they still easily fought them off, until they were summoned by the Akatsuki leader to seal the Two-Tailed Monster Cat. Hidan and Kakuzu retreated to a secluded area, where they spent three days sealing the demon cat (and in the manga another three days sealing the Three-Tailed Beast).

After the sealing was complete, Kakuzu and Hidan set out on their search for the Nine-Tailed Demon Fox's Jinchuriki (Naruto Uzumaki), only to be cut off by Team 10 (with Kakashi Hatake as the leader in place of Asuma). Shikamaru used Asuma's chakra knives to capture both the Akatsuki members in place with a trick, but Kakuzu had discovered the trick beforehand and, using a separated arm, broke free. Because of his ability to harden his skin, Kakuzu proved to be largely invulnerable to subsequent attacks. Kakashi, however, was able to analyze Kakuzu's hand seals and pierced Kakuzu's heart with his Lightning Blade, exploiting the weakness Kakuzu's earth-based jutsu had against lightning-based ones.

While this would normally be fatal, Kakuzu had five hearts (now four) in his possession, and thus recovered fairly quickly, sending a counterattack to Kakashi. Removing his cloak, he revealed four masks on his back, one of which was now broken by Kakashi. Each mask contained a heart, the broken one having given its heart up to keep Kakuzu alive. The four masks broke free from his back into separate entities, with the broken one dissolving after doing so. Each mask was able to attack with a specific and powerful elemental attack, making Kakuzu almost too much for Team 10 to handle. While Kakuzu set his sights on replacing his lost heart with Kakashi's, Shikamaru dragged Hidan away from the battlefield into some woods with his Shadow Possession Technique for a one-on-one fight.

Ignoring the other two for the most part, Kakuzu focused on taking Kakashi's heart. Though Kakashi was unable to handle Kakuzu and his mask creatures, he was saved when Shikamaru tricked Hidan into using some of Kakuzu's blood in his curse ritual, which Kakashi had collected in a capsule earlier when he pierced Kakuzu's chest and had handed it over to Shikamaru. This resulted in Hidan unintentionally destroying Kakuzu's main body's heart. Seeing this, the Lightning mask allowed it's heart to be absorbed by Kakuzu's body, bringing him back to life. In addition to that, Kakuzu also had the two other Fire and Wind masks to combine with him, making him even more powerful. He then caught the rest of Team 10 with his threads, hoping to replenish his stock.

Team 10 was saved by the arrival of Team 7, among them being the Naruto, who decided to fight Kakuzu himself, who at first did not view Naruto as a threat. This changed when Naruto unveiled his newly developed technique, Wind Release: Rasenshuriken, which Kakuzu recognized to be dangerous if it ever connected with him. Naruto's inability to maintain the technique for more than a few seconds put Kakuzu at ease, especially since it's failure almost allowed him to kill Naruto (although Yamato and Kakashi saved him), but decided to fight in his long-range mode just to be safe. As Naruto tried the Rasenshuriken once again with his shadow clones, Kakuzu attempted to crush Naruto with his threads from a distance, but was surprised to know that it was a shadow clone that he had destroyed, and subsequently, the real Naruto shoots up behind him, using the technique effectively this time.

Left with no usable hearts after being battered by Naruto's technique, Kakuzu lamented being defeated by those he considered "kids". Kakashi assured Kakuzu that the previous generation being surpassed by the next was perfectly natural and one of the "never-ending cycles of life"; Kakashi then finished him off with a Lightning Blade.

Abilities
Kakuzu was a very powerful ninja, as every opponent he had been seen defeating had been defeated with little effort. His raw strength was great enough to catch one of Choji's enlarged punches with a single hand and punch down an iron gate, as well as lifting and choking two people simultaneously. This was further supplemented by his taijutsu skills shown when during his fight with Kakashi (who was quite skilled in taijutsu himself) he mixed his hardening and extending abilities with his taijutsu.

Kakuzu was shown to be a keen analyst as well, which was somewhat attributable to his age. In the anime, he seemed somewhat more observant, easily noticing that Shikamaru was taking his time to formulate a plan to counter Hidan's technique after the former caught his partner in his Shadow Imitation Technique. He was able to quickly discern the purpose of Shikamaru's various shadow attacks and devised ways to counter them almost instantaneously during the battle.

Body Structure
All of Kakuzu's abilities revolved around his unique body structure, which was composed of hundreds of thick dark gray threads woven throughout his flesh called Earth Grudge Fear, holding his body together like stitches of a rag-doll. This allowed him to separate his body parts at will to perform long-range physical attacks and sew up almost any injury he suffers, making him very difficult to defeat. The threads could also be used to repair the bodies of others, as seen which he reattached Deidara's arm, although Hidan's inability to die after being dismembered causes him to be Kakuzu's most frequent patient. His threads could even compact together to form a giant spider-like form around his body.

Kakuzu's threads granted Kakuzu a degree of immortality (though he declines to think of it that way). The threads could pierce the flesh and bodies of others, allowing him to remove their organs and integrate them into his own body, thereby extending his life. He most commonly removed hearts in this fashion, keeping a total of five at any time and requiring that he be killed at least five times in a battle before he dies.

Five Elements
The hearts captured from ninja granted Kakuzu numerous elemental affinities and a vast supply of chakra. The raw power of each element Kakuzu demonstrated even made Kakashi, who is also capable of multiple elements, stiff with awe. The individual hearts could be released from his body and wrapped in a vast blanket of threads, forcing a heart into a limb before being detached or forming a monstrous body with a mask as its face. These masks could move and attack independently, unleashing powerful blasts of elemental chakra from their mouths.

His true chakra element is Water because he lived from a water-based village which is Takigakure (Village Hidden in the Waterfall)
 * Earth mask (Light Blue Colored): It is unknown what animal this mask is, as it was destroyed before it could be seen, but the heart has an earth-affinity. It allows Kakuzu to use Earth Release: Earth Spear and Earth Release: Iron Body Transformation.
 * Tiger-like mask (Red Colored): This heart has a fire-affinity and it takes on the shape of a demonic tiger. It can use Fire Release: Cranium Carver. This mask can also unite with the Eagle-mask to launch a fire-wind dual strike that is near unstoppable.
 * Bull-like mask (Yellow Colored): This heart has a lightning-affinity and it takes on the shape of a some sort of deformed bipedal. It can use Lightning Release: False Darkness.
 * Eagle-like mask (Blue Colored): This heart has a wind-affinity and it takes on a strange four-legged body with thin wings. It can use Wind Release: Pressure Damage. It can unite with the Tiger-mask to launch a fire-wind dual strike that is near unstoppable. But can be stopped by mixing wind and water element like when Naruto and Yamato launched the Typhoon Water Vortex Technique a combination of Naruto's Wind Release: Rasengan and Yamato's Water Release: Water Rapids.
 * Water: Using the fifth heart stored in his body, Kakuzu could use water-based jutsu. This heart's abilities are seen only in the anime, Kakuzu uses Water Encampent wall, when Shikamaru throws a Exploding badge at him.

Trivia

 * Both Hidan and Kakuzu made their first video game debuts in Naruto Shippūden: Gekitou Ninja Taisen EX 3.
 * Although covered by his hood, Kakuzu has shoulder length hair.
 * When Kakuzu first appears as a hologram at the end of Part I, he is clearly the tallest Akatsuki member there, a fact reinforced when he appears during Gaara's sealing ritual. However, when he truly appears with Hidan he is much shorter, and the 3rd databook states that he is shorter than Kisame.
 * The first kanji in Kakuzu's name (角) stands for kakugyō, the bishop in shogi.
 * Kakuzu's unusually colored eyes are similar to those of Hanzo.

Quotes

 * "Make sure he's recognizable when you're finished with him."
 * "Even Hell runs on money. I'd be just fine."
 * "Looking at your forehead protector reminds me of the very first Konoha shinobi I fought..., the First Hokage, that is."
 * (To Shikamaru) "You actually think, unlike my partner."
 * (To Hidan) "Keep talking and I will kill you."
 * (To Hidan) "Hidan, anyone with a brain would know that the world revolves around money!"