Kakuzu is a bounty hunter that is obsessed with money and often goes on side trips to cash in on bounties, much to the annoyance of his partner Hidan. Kakuzu does not like having a partner because he is prone to violent outbursts when angered and the large-scale destructive power of his techniques tend to claim the lives of his partners, however Hidan is an ideal partner due to his immortality and masochistic nature.

Kakuzu aided Hidan in capturing Yugito Nii, the young woman who contained the two-tailed cat demon. Hidan then accompanied Kakuzu to the Fire Temple that housed warrior monks. Kakuzu told Hidan that he suspected that a Jinchuuriki was there. After Kakuzu busted down the gates, they were stopped by the head monk, Chiriku, and the others. It turns out there was a very large bounty on Chiriku and that's why Kakuzu was there. After defeating all of the monks, they left with Chiriku to collect his bounty.

The two would later encountered four Leaf ninjas: Asuma, Shikamaru, Kotetsu, Izumo, Raido, and Aoba who were trying to capture the pair. Hidan wanted to fight them alone and insisted that Kakuzu didn't interfere. Hidan caught Asuma in his curse technique and slowly inflicted injuries to Asuma, but was stopped by Shikamaru before he could deal the final blow. Shikamaru forced Hidan out of the technique and Asuma cut off Hidan's head, which Kakuzu re-attached. Kotetsu and Izumo attacked Kakuzu, Izumo using "Starch Syrup Capture Field" to keep Kakuzu in one place while Kotetsu summoned a giant seashell-looking mace, but both were caught in Kakuzu's grip thanks to his extending limbs. Aoba used "Murder of Crows Confusion" to blind Kakuzu while Raido tried to cut off his head, however Kakuzu used his "Iron Skin" to protect himself. During this, Hidan once again used his curse technique to kill Asuma and the duo left.

Kakuzu and Hidan would later be caught in a trap orchestrated by Shikamaru and the team of Kakashi, Choji, and Ino. Shikamaru had Asuma's property absorbing trench knives which Shikamaru used to absorb his shadow affinity. He threw various kunais at the duo but Kakuzu used his Iron Body to defend against them, however he and Hidan were frozen in place when Shikamaru stabbed their shadows with the trench knives. Although unable to move, Kakuzu was able to remove the knifes from their shadows with his black threads, just in time to avoid Hidan's attack who was being manipulated by Shikamaru's technique. Shikamaru had Hidan continue to attack Kakuzu while Chouji attacked them both, prompting Kakuzu to once again use his Iron Body technique. Kakashi attacked Kakuzu with his Lightning Edge, piercing his Iron Body and destroyed one of Kakuzu's spare hearts, at the same time he collected some blood from Kakuzu in a vile. After Kakuzu went down, Kakashi aimed for Hidan but Kakuzu quickly swatted Kakashi aside. Kakuzu released his masked hearts with heaps of black threads for bodies and Shikamaru's technique wore off, Hidan then attempted to hold Kakashi down while Kakuzu's masked heart used it's elemental affinity to blast them, Hidan's immortality preventing him from death. However, Kakashi would escape the blast and save the team from the electrical masked heart's attack by deflecting it with his Lightning Edge, then gave the vile of Kakuzu's blood to Shikamaru who used his Shadow Imitation technique to take Hidan deep into the woods surrounded by strings attached to explosive tags.

Hidan got out of Shikamaru's Shadow Imitation and regained control of his body, allowing him to draw some of Shikamaru's blood and activate his curse technique and impaled himself in the chest... at the same time, Kakuzu's heart was destroyed just as he gained the upper hand against Kakashi. Shikamaru revealed that Hidan didn't draw blood from him, he doused Hidan's weapon with Kakuzu's blood instead. The masked hearts rushed to aid Kakuzu and, despite Chouji's attempt to stop them, the three re-integrated into Kakuzu, replacing the destroyed heart with the electric one and continued his attack, but Kakshi, Ino, and Chouji were saved by the arrival of Yamato, Naruto, Sai, and Sakura. Sai and Sakura were sent to aid Shikamaru while Yamato and Naruto remained to aid Kakashi.

Naruto used his Shadow Clones to swarm Kakuzu, but Kakuzu destroyed them and was almost struck by Naruto's new technique, Rasenshuriken. Naruto missed and Kakuzu went in for the kill, but Naruto was saved by the combined efforts of Kakashi and Yamato. Naruto used the same trick again of swarming Kakuzu with Shadow Clones to distract him so that he could try the Rasenshuriken again. Kakuzu realized that Naruto is a close range brawler and that the Rasenshurken was a dangerous technique, but also realized that it required a great deal of chakra so only the real Naruto was a threat and ignored the Shadow Clones, going straight for the kill before the Rasenshuriken could hit him... but he didn't anticipate Naruto's large chakra reserve and the one with the Rasenshuriken that he just "killed" was really a Shadow Clone and the real Naruto struck him from behind with the Rasenshuriken, destroying the two spare hearts on his back. Kakashi then dealt the final blow.

Kakuzu's body was brought back to Konoha where Tsunade conducted an autopsy.

Abilities/Techniques

He's around 100 years old and once fought The First Hokage, he is made up of the younger body parts of others that he has defeated and is held together by the seemingly endless black thread within his body. He is able to extend parts of his body by using these threads and can also extend the threads by themselves to snare his enemies. He has even used these threads to re-attach the severed body parts of his other teammates.

In the Narutoverse people's chakra possess a single elemental affinity which allows the individual to learn that specific element easier than any other. Using different elemental jutsus is done by recomposing their chakra into the element they want, which is not easy to learn. Attached to Kakuzu's back by his threads are four masks, each shielding one of four spare hearts that he has taken from enemy ninjas. He is not only able to use these spare hearts' elemental affinities, but he is able to use them to replace his heart if anything happens to it. He can also give these masks pseudo-bodies made out of his thread.

He has displayed a few elemental Jutsus, which are all large-scale and powerful. "False Darkness" is a massive electrical attack, "Intense Pain" is an immense fire attack which he sometimes junctions with "Pressure Damage," a huge wind attack, in which he uses the air to feed the flame to create an even more powerful attack. His final known technique is "Iron Body," where his body is transformed into durable iron. The element of his last heart may have been water, unfortunately Kakashi destroyed it before Kakuzu could use it's affinity.