Kakuzu, who stole the knowledge of this technique before his defection from Takigakure, was able to manipulate black threads for many purposes. He was capable of sewing up any injuries that he or others might suffer, commonly by reattaching body parts; this ability seems to instantly reattach even nerves and muscles, as the patients could instantly move their limbs without any other complex procedures right away. However, it appears that this ability is somewhat limited, as he warned Hidan not to move his head too much after he had sewed it back on, saying that it might fall off again. He could detach parts of his limbs and then manipulate them, to the point that he could even send them underground and then reattach them when he was done with them.
The most significant aspect of these threads is that they granted Kakuzu a form of immortality, although he declined to think of it that way. In addition to sewing up his injuries, he could use the threads to tear into a victim's body, steal their still functioning organs, and integrate them into his own body, thus extending his life. Kakuzu usually used this method to steal hearts from powerful shinobi, and was able to store up to four spare hearts in his body at any given time, meaning that all hearts must stop functioning in order for Kakuzu to die. He can also put one of those hearts into his limbs and have them move individually, as seen when he used his hand to remove a shadow-enhanced chakra blades that prevented the rest of his body from moving.
The extra hearts in Kakuzu's body are normally stored in various animal masks that were sewn onto his back, granting him vast amounts of chakra and numerous elemental affinities. He could detach these masks and have them take on a body of their own, composed entirely of threads. Ino Yamanaka commented the masks gave off a bad chakra. These masks were capable of attacking separately, unleashing devastating blasts of elemental chakra. These threads could also compact together to form a spider-like body around Kakuzu, allowing him to fuse the attacks of his masks together in order to increase his attacking power.
Kakuzu's animal masks contained his spare hearts. If he took use of the heart for himself, the corresponding mask would shatter upon the creature's reentry into Kakuzu's body.
- Fire mask: This heart had a fire-affinity, and took on the shape of a demonic tiger. It could use Fire Release: Intelligent Hard Work. This mask could also unite with the Wind mask to launch a fire-wind dual strike that was near unstoppable.
- Lightning mask: This heart had a lightning-affinity, and took on the shape of some sort of deformed bipedal. It could use Lightning Release: False Darkness.
- Water mask: This heart had an water-affinity, and took on the shape of a demonic, beaked bipedal. It allowed Kakuzu to use Water Release techniques, although they were not seen as the mask was destroyed before Kakuzu could use any.
- Wind mask: This heart had a wind-affinity, and took on a strange four-legged body with thin wings. It could use Wind Release: Pressure Damage. It could unite with the Fire mask to launch a fire-wind dual strike that was near unstoppable.
- Like the rest of Kakuzu's techniques, the name of this techniques comes from the mecha anime Mobile Suit Gundam (機動戦士ガンダム, Kidō Senshi Gandamu). The name Jiongu was taken from the Mobile Suit MSN-02 Zeong (ジオング, Jiongu), a mecha that can detach its arms for ranged attacks, while still attached to the main body with wires. The name was altered slightly and given kanji to create the name of this technique.