Kakuzu

is a fictional character from the manga series Naruto. The first kanji in Kakuzu's name (角) stands for kakugyō, a bishop in shogi.

Background
Kakuzu is a missing-nin from Takigakure and Hidan's partner. Kakuzu is the longest-lived known character in the series, having lived at least since the time of the First Hokage, whom Kakuzu mentions having fought at one point (he doesn't elaborate on the outcome).

Hidan and Kakuzu display the most animosity towards each other out of all members of Akatsuki, neither being very fond of the other's interests. The two often trade barbs with one-another, Kakuzu's usually being better timed than Hidan's. Hidan gets annoyed 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 his head. Kakuzu, in turn, dislikes Hidan's religion, believing the rituals associated with it to be a waste of time, and is also impatient with Hidan's drawn-out speeches and battle style. The reason Kakuzu deals with Hidan is because he's quick to anger, and will often kill anyone in sight when enraged. Hidan is the perfect partner for Kakuzu because of his apparent inability to die. Kakuzu's somewhat indiscriminate attack style also makes Hidan a perfect partner, since Kakuzu need not worry about catching his partner in the crossfire.

Kakuzu is a greedy individual, often arranging goals in terms of the highest profit he can gain from them, something his partner cannot stand. He even comments on money being the only dependable thing in the world and that he wouldn't mind going to hell because money probably runs it. Due to this view of money, he refers to himself as the Treasurer of Akatsuki. Given his friendly relationship with a bounty officer, it would seem he collects bounties rather frequently to earn cash, and does so (or at least tries) during his missions on several occasions, which is another point of infuriation for Hidan. He even looks at Hidan's religion through his ability to earn money from it, which is why he puts up with it.

Despite his obsessive personality and violent rage, Kakuzu is much more cautious than his partner, frequently warning Hidan to not let his guard down then teasing him when he inevitably does. Kakuzu is shown to be a keen analyst, as well, which is at least somewhat attributable to his age, which, by extension, gives him several lifetimes of battle experience. He was able to quickly discern the purpose of Shikamaru's various shadow attacks and devise ways to counter them almost instantly during battle, to name one situation. He also seems to be more willing to take 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 gotten on Asuma Sarutobi at the time. However, he does make it a point to retrieve the case with his bounty. He seems to forget the greater goals of the organization when enraged, however, as he attempted to kill Naruto in spite of Akatsuki's need to capture all the tailed beasts alive.

Abilities
Kakuzu has a unique body structure that consists largely of a thick, black thread. He can control the thread at will and it runs throughout his entire body, connecting him together like a rag doll. This unique body structure allows him to integrate foreign organs into his own body, provided they are functional while he's doing so. Kakuzu uses this process to integrate the hearts of others into his own body, prolonging his life indefinitely. He keeps a supply of five hearts at any given time, making the chance of his hearts all failing unlikely at best. Kakuzu's four extra hearts are normally attached to four masks sewn onto his back, each one resembling a demonic animal (an eagle, a lion, and an ox are the visible ones). When one of his hearts is worn away naturally or is destroyed, he can simply replace it. The length of time in which Kakuzu has being doing this is unclear, but the fact that he battled the First Hokage at some point means that he is at least in his seventies.

Aside from granting him effective immortality, Kakuzu's threaded body allows him to repair his own injuries or attack from a distance by stretching the thread attached to his limbs. Using the hearts in his body, he can even detach his limbs and control them remotely. Kakuzu's threads can also be used to reattach the severed limbs of others. There is apparently no limit to the amount of thread Kakuzu can create, as he transforms himself into a massive, spider-like creature shortly before his defeat.

Kakuzu's most powerful abilities lie in chakra manipulation. Having four extra hearts, Kakuzu can manipulate chakra in each one, allowing him to utilize every type of element for offensive purposes. He does this by separating the four masks on his back, which grow into animal-like thread creatures capable of utilizing a specific element: the eagle uses wind, the lion uses fire, and the ox uses lightning. These bodies can merge together to allow combination elemental attacks to be used. The masks are maintained by the hearts within them and shatter should the heart be destroyed or removed. Kakuzu can do this willingly in cases where his active heart is destroyed.

Finally, Kakuzu has an earth-based jutsu that hardens his body, increasing his strength and rendering him virtually invulnerable to any physical attack. So far, only Kakashi Hatake's Lightning Blade has been able to beat this technique, which is due to the natural weakness that earth-based jutsu have to lightning-based jutsu. It's not clear if the broken mask is responsible for this technique or if Kakuzu has a natural affinity towards earth.

Team 10 arc
Kakuzu first appears with his partner, Hidan, in their pursuit of the two-tail's host, Yugito Nii. She allows herself to be cornered in order to spring a trap on them and eliminate them herself. Yugito transforms into her full demon form, a large flaming cat, after Hidan provokes her, which annoys Kakuzu. He claims Hidan has just made their job more difficult. Despite her efforts, the two defeat her and Zetsu arrives after to drag her off. Kakuzu then notes their next target to be in the Land of Fire. In spite of the implication, they are apparently not chasing Naruto, as indicated by a later conversation with Deidara.

On their way, Kakuzu decides to attack a temple in order to collect the bounty on the head monk, Chiriku, who was a former bodyguard for the Fire Country's nobility. He is listed in the bingo book with a three million ryō bounty. They slaughter most of the other monks, but one escapes to warn Konoha of the incoming threat. While the Niju Shotai are mobilized to deal with the pair, Kakuzu is stuck carrying the head monk's corpse.

One Niju Shotai team consisting of Asuma Sarutobi, Shikamaru Nara, Kotetsu Hagane, and Izumo Kamizuki catches up to the pair at a bounty station, where Kakuzu is cashing in the deceased monk. For the most part, Kakuzu lets Hidan fight, only intervening when Shikamaru deduces the purpose of his curse jutsu and disrupts it, allowing Asuma to decapitate Hidan. Being immortal, Hidan survives, and Kakuzu repairs the wounds using the threads in his body. He then fights with Kotetsu and Izumo, easily holding the two off while Hidan deals a fatal blow to Asuma. Their battle is interrupted by the appearance of another Niju Shotai team, this one consisting of Ino Yamanaka, Choji Akimichi, Aoba Yamashiro, and Raido Namiashi. Kakuzu is unwilling to leave Asuma behind, since Asuma has a substantially higher bounty than the monk he just cashed in, but is forced to retreat by the Akatsuki leader, who wants to seal the most-recently captured demons.

After the sealing is complete, Kakuzu and Hidan set out on their search again, only to be cut off by Team 10 with Kakashi Hatake in place of Asuma. Kakuzu habitually notes that Kakashi has a high bounty. A clever move by Shikamaru pins both Akatsuki members in place, but Kakuzu catches onto the trick beforehand and breaks free using a separated arm. Because of his ability to harden his skin, he proves largely invulnerable to subsequent attacks. Kakashi, however, is able to pierce his heart with his Lightning Blade, exploiting the weakness Kakuzu's earth-based jutsu has against lightning-based ones.

While this would normally be fatal, Kakuzu has five hearts (now four), and thus recovers fairly quickly. Removing his cloak, he reveals four masks on his back, one of which is now broken. Each mask contains a heart, the broken one having given its up to keep Kakuzu alive. The four masks break from his back into separate entities, the broken one melting after doing so. Each mask is able to attack with a specific and highly powerful elemental attack, making Kakuzu almost too much for Team 10 to handle. While he sets his sights on replacing his lost heart with Kakashi's, Shikamaru drags Hidan away from the battlefield for a one-on-one fight.

Ignoring the two for the most part, Kakuzu focuses on taking Kakashi's heart. He does note that Shikamaru could have collected an impressive bounty had he lived longer (he believes Shikamaru is doomed). Though Kakashi is unable to handle Kakuzu, he is saved when Shikamaru tricks Hidan into using some of Kakuzu's blood in his curse ritual (Kakashi had collected it earlier when he pierced Kakuzu's chest). Though slowed, Kakuzu adapts quickly, dragging another heart from one of his masks to replace the lost one. He then catches the rest of Team 10 with his threads, hoping to replenish his stock.

Team 10 is saved by the arrival of Team 7, consisting of Uzamaki Naruto, Haruno Sakura, Yamato, and Sai. Naruto decides to fight Kakuzu himself while Sakura and Sai are sent to help Shikamaru. Kakuzu is able to identify Naruto thanks to his earlier conversation with Deidara, and is not concerned at first. This changes when Naruto unveils his Wind Release: Spiraling Shuriken, which Kakuzu recognizes to be dangerous if it connects. Naruto's inability to maintain the technique for more than a few seconds puts him at ease, especially since its failure almost allows Kakuzu to kill Naruto (Yamato and Kakashi save him), but he decides to fight long range just to be safe. Using his threads, he attempts to crush Naruto from a distance, but is surprised when the real Naruto shows up behind him, using the technique effectively this time.

Left with only one usable heart after being battered by Naruto's technique, Kakuzu laments being defeated by those he considers "kids." Kakashi assures him that the previous generation being surpassed by the next is perfectly natural; Kakashi then gathers lightning in his hand and finishes Kakuzu off.