Orochimaru Ninja Genius from Konohagakure

Technically, Orochimaru is the only ex-Akatsuki member (official) who is still alive in the Next Generation series (Chapter 700 - After Boruto: Naruto The Movie).

Source: Narutopedia

Orochimaru is a genius Shinobi and full of mystery. He has a very wide knowledge of the world of shinobi along with its dark side and rottenness. He is the type of person who will do everything possible to realize his desires, not to mention doing dirty things that may also risk his safety.

Although Orochimaru is often 'Dead' and sealed, due to his genius and cunning, he can still live up to an era far from his heyday. He is also one of the remaining Sannin Legends besides Tsunade. If Tsunade has a legendary healing Jutsu (regeneration), so as to keep his appearance younger in his old age, Orochimaru himself has an 'extreme version' of the ageless jutsu Fūshi Tensei.

By using the body of others as a 'container' for his soul, Orochimaru was able to survive longer than the average human life. In addition, the reason why Orochimaru was still alive in the Boruto era was that he had a 'trick' to keep his soul from being 'lost' even though he was killed.

As mentioned before, Although Orochimaru is often 'dead' or sealed during the fight, his soul will still exist and still have the potential to bounce back at any time.

In the middle of the Fourth Shinobi World War, Sasuke who wanted to seek a truth tried to revive Orochimaru from his long sleep using the Kaija Hōin technique. In simple terms, the technique still belongs to the Fūinjutsu category is the opposite of the Fūja Hōin (Jutsu) Technique that Kakashi once used to suppress Orochimaru's invisible seal in Sasuke's body.

If Fūja Hōin requires a fairly complicated preparation and impressed hard to use at a sudden time. Instead, Kaija Hōin is more impressed simple and easy to do if indeed the requirements have been obtained. With the help of Orochimaru's cell on Kabuto's body, Sasuke imprinted it on the magic seal through Jugo's help. Then he chants a handful of hand seals opposite to Fūja Hōin's hand seal to release and summon Orochimaru's remaining Soul in Ten no Juin of Anko.

⚜ Fun fact: Orochimaru is the only person known to have ever called Shiki fūjin, but has survived to this day.