Kakuzu (Šp“s, Kakuzu) is a missing-nin from Takigakure and Hidan's partner. He is a greedy individual, prioritizing things in terms of how much they are worth and finding money to be the only thing that he can depend on. Kakuzu's favorite source of income is collecting bounties, and he has even memorized the worth and information on some of the more dangerous targets. Due to this view of money Kakuzu refers to himself as the "Treasurer of Akatsuki", though it is unknown if this is an actual position. Despite finding Akatsuki to be a good source of income Kakuzu greatly dislikes the fact that he needs a teammate, due in part to his habit of killing anyone near him (partners included) when enraged. Having killed all of his previous partners as a result of this, Kakuzu was partnered with Hidan. Although neither enjoys being paired together Hidan's inability to die makes him the ideal teammate for Kakuzu.

Kakuzu's body is composed of a great deal of thick black threads that he can use to detach his limbs for long-range assaults. The threads themselves are also capable of piercing flesh, which Kakuzu uses to remove the still-living organs from his enemies. Once he has done so Kakuzu can integrate these younger, healthier organs into his body that, in theory, allow him to extend his life indefinitely. Kakuzu most prominently uses hearts in this way, keeping up to four extra hearts with him at any given time. He keeps these spare hearts stored within animal masks sewn to his back, and each of the masks can separate from his body and attack independently. Once removed from his body the masks can shoot powerful elemental blasts at opponents, three of which being fire, wind, and lightning. If the heart in Kakuzu's body is destroyed one of the masks can remerge with him so that he can take use of its heart, causing the mask to crumble away. Kakuzu also has an earth-based defensive technique that makes him virtually immune to physical attacks, though it is unclear which of his hearts this ability is attributed to. Kakuzu's masks are slowly destroyed at the hands of a group of Konohagakure ninja; Naruto Uzumaki is even able to destroy two of his hearts simultaneously and bring a third to the brink of failure. Although Kakuzu survives Naruto's attack he is left unable to move, allowing him to easily be finished off by Kakashi Hatake.