In the narutoverse, Orochimaru would be the go-to immortal. Yet, Madara claimed he had attained the power of an immortal just after absorbing the Holy Tree. Kaguya could also be considered a true immortal after she had eaten the fruit and siphoned chackra from the entire planet. Obviously, the general theme of the Akatsuki was a 'collection of immortals', but as Kakuzu admitted, none of them were truly immortal.
In other media, this theme is shared. FMA:
DBZ:
Jupiter Ascending:
Common theme? In all of these cases, sacrifices were required in order to attain immortality. In 3 of the 4 cases, this immortality equated to massive levels of power, some considered godly. The re-occurring theme becomes immortality is attained from combining the power of thousands or millions of humans into one being. Along with this immortality typically comes power at a comparable magnitude.
I found this idea quite interesting and its a scary though trying to attain immortality in such a way. These are all the examples I could think of given what I've seen. If you have any additional examples or similar stories/ themes please don't hesitate to point them out to me. Thanks for reading.
In other media, this theme is shared. FMA:
In Fullmetal Alchemist, both Hohenheim and Father were immortals. Hohenheim contained a Philosipher stone on the order of 500,000 people. Father's philosopher stone was much larger, and while I couldn't find an exact number of souls contained in it, I seem to recall it was on the order of hundreds of millions. Father's power was also unmatched and likened to a god quite clearly in the manga. This is very similar to Kaguya, yet his magnitude of power was arguably on a whole other level.
DBZ:
Cell. Cell was created using the DNA of multiple combatants. More importantly, his objective in life was to absorb the essence of others. First he started by absorbing thousands of people. Later he absorbed Androids 17 and 18. This was not unlike the collection of souls for the philosopher stone or the binding of countless prisoners via the Holy Tree.
Jupiter Ascending:
A reasonably recent movie, this was a fantasy title that's story was about humans originating on another planet. Later colonizing earth, the elite families of the origin race populate and cultivate off branches of humans on other planets. Once up to their standards, these elite families kill all the residing humans and convert their bodies into a concentration of plasma-like essence. This essence can be utilized in massive quantities to rejuvenate cells in the form of a bath. This form of immortality forced the slaughter of millions.
Common theme? In all of these cases, sacrifices were required in order to attain immortality. In 3 of the 4 cases, this immortality equated to massive levels of power, some considered godly. The re-occurring theme becomes immortality is attained from combining the power of thousands or millions of humans into one being. Along with this immortality typically comes power at a comparable magnitude.
I found this idea quite interesting and its a scary though trying to attain immortality in such a way. These are all the examples I could think of given what I've seen. If you have any additional examples or similar stories/ themes please don't hesitate to point them out to me. Thanks for reading.