Let’s begin with one of the most popular and iconic characters in the series, Orochimaru the snake man. The thought of immortality entered Orochimaru’s mind right after he lost his parents because of the war. He pondered the idea of life without death all the way until he graduated into a proper shinobi. Once he goes through all kinds of difficult missions, earns the title of one of the three great shinobi, and becomes a member of Konoha’s Black Ops organization, Orochimaru finally begins to put that idea into practice.

The method that he finally found is actually one of the most difficult ways to obtain immortality, especially compared to the other shinobi in the series. Because his technique requires him to transfer his consciousness, along with his memory, knowledge, and everything that comes with it, into a new body. This means in order to stay immortal, Orochimaru would need to find a new body every time his current one is no longer viable to use.

Needless to say, finding a strong body that can provide the necessary amount of chakra and withstand the burden of his jutsu is also a crucial part of Orochimaru’s Immortality ritual, which adds another layer of difficulty to this already cumbersome process. Another important note is Orochimaru’s immortality is focused solely on eternal life, which means he can still be killed just like any other normal, albeit way stronger, human.

Hidan is actually the closest person to true immortality in the series. The reason is that he simply cannot die. You can stab him, poison him, or even decapitate his head, and he will still be alive. He can feel the pain, but any kind of wound inflicted on his body will simply heal on its own. It’s unclear whether he will grow old or stay young forever, but it is said that the only thing that may have the chance to kill him is starvation.

As for the source of his immortality, well, Hidan said that his power is a blessing from his God, an entity called Jashin. The truth, however, is a bit more complicated than that. You see, Jashin is actually a cult that grew in Hidan’s hometown, Yugakure, that worships the aforementioned God, also named Jashin. Jashin’s creed is to indiscriminately kill and destroy as much as possible. The young Hidan, who already has a warped mind at the time, finds out about the cult and becomes obsessed with it.

As a matter of fact, he believes that he is the most faithful member of the cult, which leads to him learning everything that is to know about Jashin. Taking things further than that, Hidan also experimented with the hidden Jashin’s technique in his own body. It’s unclear what precise procedure he used or the jutsu that he cast onto himself, but one thing is for sure, he came out of it with an undying body.

Kakuzu is the oldest active shinobi in Naruto. According to him, he has been around since the time of the first Hokage, Hashirama Senju. He even gets the chance to engage in a battle with the aforementioned legendary shinobi. So yes, he is a proper immortal indeed. However, the method by which he obtained his immortality is vastly different from the two mentioned above. It’s actually more akin to a medical procedure, rather than a ninja technique.

You see, Kakuzu obtains immortality by transplanting a new heart whenever he thinks that his current one is no longer able to sustain his life. And just like Orochimaru, he prefers the heart of a strong shinobi, usually, the one that he killed himself, over regular people. Because that kind of person usually has a much stronger heart than common folks.

As if that’s not shocking enough, Kakuzu actually goes even further than that. In order to strengthen himself, Kakuzu transplants four other hearts into his body, each with different chakra attributes. This allowed him to use all five chakra attributes at the same time. It also means his enemy has to kill him five times or destroy all five hearts at the same time if they want to kill him. And as we’ve found out from the series, there’s only a handful of people that can do that in the whole series. And that is also one of the reasons why he can still freely roam the earth after all these years.

Sasori’s obsession with immortality roots in the same feeling of despair and anguish as Orochimaru. Because he also lost both of his parents at a young age and has to grow up feeling lonely and depressed. In order to cheer him up, Sasori’s Grandmother, who happens to be the strongest Kugutsu (Ninja Puppets) user in the history of Sunagakure, introduces him to the art of Kugutsu.

Unbeknownst to her, Sasori becomes instantly obsessed with Kugutsu. He learns everything there is to know about art, and masters them all in no time. It doesn’t take long for Sasori to begin crafting his own puppets, the first of which includes a pair of puppets that resembles his own parents. As he goes deeper into his obsession, Sasori begins to lose sight of what’s right and wrong.

That is when Sasori successfully created puppets that are made out of real human bodies, called Hito Kugutsu. This new kind of puppet allowed Sasori to use the chakra of the real body and even cast their unique Jutsu, such as the fourth Kazekage’s Iron Sand technique. And as the final step, Sasori began to turn himself into a puppet. At first, he started with his limbs, but his experimentation gradually got more extreme to the point of becoming a full puppet himself, with only a little part of his flesh and blood embedded into the scroll on his chest. And that is how Sasori becomes immortal.