Immortality has been the goal of many Shinobi in Naruto. But very few were actually able to achieve immortality. All Jutsu that granted immortality to a person were termed as Forbidden.
Here’s a list of all the 6 Immortality techniques in Naruto.
6. Kakuzu’s Forbidden Technique
So let’s begin with Kakuzu. Kakuzu had a unique ability, called the Earth Grudge Fear, that allowed him to live forever, by stealing the hearts of people. Kakuzu once tried to assassinate Hashirama, but failed.
The important thing to notice is that he emerged from the battle alive. Later, he went back to his village and killed all the elders and stole their hearts.
Later, he was recruited y the Akatsuki for his immortality technique.
He could also reattach body parts with black strings and use them to steal the heart of a person.
Kakuzu can technically live forever, but only if he is able to steal hearts freely.