Kāma

Kāma is a seal that serves as a compressed backup of an Ōtsutsuki clan member's biological data that they can embed in the body of a chosen recipient, transforming them into a for the Ōtsutsuki's will should they sustain fatal injuries. Over time the Kāma overwrites the vessel's genetic profile until their body transforms into that of a perfect recreation of the Ōtsutsuki template, at which point the Kāma disappears and the Ōtsutsuki can take over their body and.

In the interim, the vessel can learn to activate the Kāma and utilise a portion of the Ōtsutsuki's power and abilities, at times even allowing the Ōtsutsuki's will to manifest and take control over their body.

Appearance
Though the Kāma superficially resembles a tattooed seal, it is actually a pyramid-shaped barb that is embedded in the vessel's body. Upon activation the visible marking will spread across the vessel's body, at times taking on different patterns depending on the abilities being used. Typically black, these markings may also shimmer and glow with a particular colour when activated, and when viewed up close appear to spread in patterns resembling microscopic circuitry.

Isshiki Ōtsutsuki

 * Jigen: Isshiki embedded his Kāma into Jigen's chin while parasitically fused with his brain, after being betrayed and nearly killed by Kaguya Ōtsutsuki. When activated it spreads across his face and body in nearly symmetrical sunburst patterns. Progressing further, he sprouts a long horn identical to Isshiki's. He lost this Kāma after Isshiki was forced to reborn through his body.
 * Kawaki: Upon realising that Jigen's body would not be able to sustain his chakra, Isshiki transferred his Kāma into Kawaki's left palm through scientific experiments conducted with the aid of Amado. When activated it spreads across the left side of his body forming a pattern that almost perfectly mirrors Boruto's, extending up to his left eye, and then glows red. Progressing further, he sprouts a short horn resembling Isshiki's. He lost this Kāma when Isshiki resurrected via Jigen's body, but later gained another one under unknown circumstances.

Momoshiki Ōtsutsuki

 * Boruto Uzumaki: Momoshiki embedded his Kāma into Boruto's right palm as the boy dealt a fatal blow to him using the Parent and Child Rasengan. When activated it spreads across the right side of his body forming angular and curving geometric patterns, extending up to his right eye, and then glows blue. Progressing further, he sprouts a horn similar to Momoshiki's and his right eye turns into a Byakugan.

Abilities
When activated, Kāma significantly enhances the user's physical abilities and the power of their jutsu, and can absorb chakra and chakra-based attacks like ninjutsu. Kāma can also be used as a medium for Space-Time Ninjutsu, opening rifts to any location including foreign dimensions at will. This ability seems to be rather advanced as only Jigen was able to use it by himself, Boruto and Kawaki's needing to cooperate to use it instead.

Boruto's and Kawaki's Kāma exhibit when in close proximity. When their Kāma resonate, it apparently enables them to release anything that either of them had previously absorbed. This resonance seems to be coming from Kāma that are acquired from different sources, as Kawaki got his from Isshiki (via Jigen), while Boruto got his from Momoshiki. Jigen and Amado theorised that it was this resonance that allowed both Kawaki's and Boruto's Kāma to mature more rapidly than expected. Although Jigen is able to synchronise with Kawaki's Kāma to open a space-time rift, no such resonance exist between the two of them as Kawaki did not experience the sudden growth until his contact with Boruto.

Kawaki could activate it at will by the time he first met Boruto and three years later, Boruto was able to activate the seal at will as well, while Jigen was fully capable of activating it any time he desires. Boruto's resonated Kāma could also be forcefully activated when Kawaki activates his own nearby.

Through the aid of science, Isshiki was able to transfer his Kāma from Jigen to other individuals, albeit with a low rate of success, as of fifteen known test subjects, thirteen are confirmed to have died, with Kawaki the only known successful recipient. Jigen has also shown the ability to absorb chakra from creatures that are similar to tailed beasts and force Kawaki's Kāma to synchronise with his for him to open a portal to his location.

Manifestation
Under certain circumstances the Ōtsutsuki can manifest their will to possess the body of the vessel, causing the markings to change shape and the surrounding portion of their body to transform, undergoing changes that may include protruding Ōtsutsuki's signature horns and even activating their dōjutsu. This seems to only be possible after a great deal of time or as a result of resonance, and typically occurs during moments of heightened emotion or stress.

While Jigen can activate this state freely, Kawaki was only able to partially achieve it out of anger, with Jigen surprised by how quickly it progressed. Likewise, Momoshiki was only able to manifest through Boruto's body when the boy was knocked unconscious and nearly killed by Boro. Extended use of this form can greatly wear down the vessel's body: Momoshiki had to absorb Naruto's chakra to continue fighting until he killed Boro in Boruto's body and he soon collapsed. Additionally imperfect vessels can break down from the sheer power the Ōtsutsuki was using, as though Jigen could activate it willingly, he was unable to handle Isshiki's full powers for long and began breaking down after a while.

Resurrection
Over time, the vessel's own genetic information will be completely overwritten by the Ōtsutsuki biological data accumulated in the Kāma, at which point the Kāma will disappear and the Ōtsutsuki will resurrect, taking over the vessel's body and erasing their personality. This is the true purpose of Kāma, and allows the Ōtsutsuki to transcend death. Even if the vessel's body dies and is severely damaged, so long as it exists and still bears Kāma, it will remain viable for the Ōtsutsuki to resurrect through, in which any damage it has suffered will be healed.

Amado noted that there is no known way of removing a Kāma from a vessel, nor to stop its takeover, aside from killing the vessel before the resurrection process completes itself; even the very Ōtsutsuki who placed the seal onto the vessel cannot control the automatic transfer. However, the Kāma's final process of resurrection will not occur so long as the Ōtsutsuki in question is still alive, hence Isshiki was not reborn through Jigen's body despite the Kāma already having extracted all the data into Jigen's body. At the same time, a non-suitable vessel can be used to perform an imperfect resurrection of the Ōtsutsuki. Upon being resurrected, should there be any other Kāma implanted by the same Ōtsutsuki, those additional Kāma will simultaneously be completely erased. Amado speculates this is a feature to prevent duplicate incarnations of the same Ōtsutsuki.

Drawbacks
Imparting a Kāma onto a candidate vessel requires a huge amount of energy to do so; when Isshiki was fatally injured by Kaguya, he did not have enough strength to apply one to Jigen at the time. While applying one onto the unsuitable Jigen seems to have no immediate detrimental effects on his body, when Isshiki attempted to do it again on fifteen children via scientific aid, at least thirteen of them died due to incompatibility. Although Kawaki noted how painful it was when he was subjected to Isshiki's process, Boruto did not show any suffering when he received the Kāma from Momoshiki.

As Amado noted, the most important factor of applying Kāma is the selection of the vessel; if an Ōtsutsuki uses an inadequate vessel for a revival, the body will be unable to handle the enormous chakra, and most likely die within a couple of days. Compatibility seems to be rare, as out of the fifteen children Isshiki attempted, Kawaki is the sole success, and Isshiki himself noted how Boruto's affinity with Momoshiki's Kāma to be uncommon.

Once the Kāma is applied, its process of spreading the biological data into the vessel and the final resurrection initiates automatically, in which not even the caster can control it. When an Ōtsutsuki resurrects, the vanishing of duplicate Kāma means they're vulnerable to a permanent death unless they can apply another Kāma, especially if forced by circumstance to resurrect in an imperfect vessel.

Using Kāma in battle could prove taxing for less skilled users, even more so when they are already weakened, as Kawaki quickly collapsed after using it against Garō as he was already injured from defeating Kara's robots while Boruto was left so badly weakened after using it for the first time that he collapsed and had to be helped to return to Konoha. Additionally, activating it seems to cause a not sufficiently experienced user some pain, as Boruto expressed pain whenever he activates Kāma. Jigen doesn't seem to suffer these weaknesses as he is much more capable at using them than either Boruto or Kawaki, as he never showed any reaction when activating Kāma and using it in his prolonged battle with Naruto and Sasuke had no effect on him. However, one known weakness of the seal that even Jigen seems to suffer from is that incomplete vessels could breakdown from channelling Kāma's full power, as after overpowering Naruto and Sasuke, the blackened section of his body cracked and he even cried soon afterwards and was forced to retreat back to be treated by Amado.

Kāma can only absorb chakra-based substances, hence the wielder is vulnerable to non-chakra matter and energy such as viruses and natural flames.

Trivia

 * Though its furigana reading indicates the pronunciation, its kanji spelling is given as , a Japanese tool resembling a wedge or linchpin, and its full appearance when not embedded in a host's body has a similar appearance and function.
 * "Kāma" means "wish", "desire", or "longing" in Hindu literature, and in Japanese it is also an uncommon way to write "karma." The latter is used as its official translation in Western media.
 * Sarada Uchiha has theorised, due to their similar appearance, that the Strength of a Hundred Seal may be related to it.