Why I Wrote This: Ever since Kishi has been introducing more characters who claim immortality, I was curious if Kishi is planning on introducing someone who is a true "immortal". In other words, a person who is born with such a thing, and who does not have to use artificial means to achieve such a state (like Sasori and Orochimaru for example). When you actually give some thought into such a possibility, it isn't too farfetch'd for Kishi's ever-active imagination. (Note--The words immortality/invulnerability/invincibility/etc. are assumed to have the same meaning in my post since people interchange the words all the time around here.) Artificial Immortality In the narutoverse, several characters have achieved "immortality", and thus, next-to-impossible to vanquish. Such examples include: Sasori--Hitokugutsu This technique allows Sasori to turn a still living human into a puppet. The puppet will maintain the same amount of chakra as its original body held while still alive, and other unique traits, like genetic abilities, will be preserved. Sasori used this technique, or a variation of it, to turn himself into a living puppet. The only way he could be vanquished was by attacking the container which held his heart, and it was this weakness that spelled his downfall at the hands of Chiyo + Sakura during Sasori's final battle. Orochimaru--Fushi Tensai This technique prevents Orocharimu's death by allowing his soul to linger in the material world, thus allowing him the capability of transferring his mind from container to container. Orochimaru himself is no longer bound by the physical limitations time places upon the human body, but he must inhabit his host for a number of years before he can leap-frog to another body. Tsunade--Souzou Saisei When the seal on Tsunade's forehead is dispelled, the released chakra disperses and stimulates the proteins of her body to increase the speed of cell division and reconstruction of cells. This alllows her to recreate major organs and/or tissues. Still, her technique does not regenerate her prior cells, and causes the body's cells to come closer to aptosis. Note--This technique is meant for immortality in battle only. Kabuto-- In'yu Shōmetsu Kabuto gathers healing chakra to a place of injury and begins to regenerate; this technique can even rekindle dead cells. Hidan's Immortality Until the manga disproves me, I'll assume Hidan's immortality is as unnatural as everyone else's so far. So far, we know that he can survive decapitation, Kakuzu's monstrous-strength punches, and blows to the vital areas. However, the key to his immortality is unknown for the moment. As I've pointed out, Kishi has already added the concept of "pseudo-immortist" to his work, so it is not impossible for him to expand on the subject, and actually develop a character who is a natural-born immortal. Applications of Real-Life Kishi would have plenty of material to work with in reality if he wanted to make a true immortal, like the Highlander series for example. If Kishi were to do such a thing, perhaps the best clue(s) to how he would have it function would probably involve cellular division. As we already know, cells can divide so many times in a lifetime before the cell finally goes splat. Did you know that this concept is far from true because human cells are quite capable of multiplying endlessly. As a matter of fact, there is a medical term for such phenomena: Cancer. Cancer can be defined as uncontrolled, non-stop cellular division that ultimately kills you because it will eventually kill parts of the body by hogging all the criticial materials for a cell to live, like oxygen and glucose for examples. Now, a cell becomes cancerous because of mutations that occur within the DNA. Normally, the genes that control cell division go out the window, and next thing we know, the cell becomes the local pimp of the cell neighborhood. Wait a minute...did someone say mutations in DNA? Doesn't such a thing exist in the narutoverse? OH MY GOD, BLOODLINES ARE MUTATIONS OF DNA! To put it simply, the immortality kekkai-genkai would act like a "controlled cancer", perhaps controlled via chakra. Besides, Kishi has done several examples of bloodlines that allow the user radical abilities because of mutations in the cellular structure of the individual. Kishi hasn't done it once, but twice: Shikotsumyaku The kekkei-genkai of the now extinct Kaguya Clan, which gave them the frightening ability to manipulate their own bone structure. As Kimimaru demonstrated in his fight against Gaara, the bones could be protruded out of the body, bones could be fired from the fingertips, and bone armor could be created under the skin. This kekkei-genkai makes the body virtually indestructable via physical means, giving the user a nearly perfect defense. Soume no Kou The kekkei-genkai of the brothers Sakon and Ukon; this genetic ability allows the two brothers to break down their body at the molecular level and merge with each other. When the true potential of this bloodlines is achieved though, it is possible for the brothers to separate and fuse to another person's body. As you can see with these two bloodlines alone, Kishi can easily allow a person's ability to replicate its cells endlessly, allow a user to regenerate life-threatening wounds in mere seconds. Also, keep in mind the fact that genetic engineering does exist, as proved by the case of Yamato. Candidates: Akatsuki: Since Akatsuki appears to be an Immortality Club, why not? We know next to nothing about AL and BH, so there isn't any harm in speculating their abilities until the manga confirms/ruins the moment. Kabuto: Once again, why not? When Kabuto remarked to Tsunade that he had the ability to reactivate his dead cells, Tsunade, one of the world's leading medical experts, was shocked that such a thing could be done. Naruto: Kishi has shown us on several occassions that Naruto's regenerative abilities are astounding. He can heal a Chidori to the lung in mere seconds, and his body can regrow its skin after a few minutes after KN4 finally subsides. Lastly, remember too that Naruto's kyubi chakra acts 99.99% identical to the Cursed Seal, a way for a person to maximize his or her own potential, including kekkei-genkeis. Also, remember how the Kyubi chakra only enhances Naruto's physical abilities, so if he was indeed born with a regenerative kekkei-genkei, the Kyubi chakra would allow it to reach its full potential, but unfortunately, appear to be solely responsible for the regeneration as well. Conclusion: It isn't too farfetch'd for Kishi to introduce an ability that allows a person to be naturally born with the potential to far outlive the typical human lifespan. If he were to do such a thing, it would probably act similar to Kabuto's/Naruto's regenerative capabilities. Lastly, such a kekkei-genkei would kick-ass pretty much. Hoped you enjoyed the reading.