It could be Itachi. Even though Itachi has his own complex past, he is highly skilled in Anbu - like operations. He could show Naruto the ropes of the Anbu world, teaching him how to analyze situations quickly and make tough decisions that are often required in Anbu missions.
Another option could be Yamato. Yamato is known for his calm and collected nature. He could help Naruto control his chakra better in the context of Anbu stealth operations. He could also be a good mentor in terms of teaching Naruto how to work within a team in the Anbu, which is different from his usual team dynamics.
One possibility is that Naruto joins the Anbu to prove himself even more. He might face challenges like learning the stealthy ways of the Anbu which are very different from his usual open - combat style. He could also be sent on dangerous solo missions that test his limits both physically and mentally.
In this fanfiction, Kakashi could also be Naruto's mentor in magecraft. Kakashi is known for his adaptability. He could start to study mage powers along with Naruto. They could learn together about new forms of magic, and Kakashi could use his combat experience to help Naruto understand how to use his mage powers in battle situations.
Iruka could be his mentor. Iruka has always been there for Naruto from the start. He could teach Naruto the basics of swordsmanship, using his knowledge of the ninja arts. Iruka would be patient and understanding of Naruto's blindness, helping him to develop other senses to compensate for his lack of sight.
Maybe Tsunade. She is known for her love of sake. She could have some hidden knowledge of the Drunken Fist. Since she is also a very powerful ninja, she could train Naruto in both the physical and strategic aspects of the Drunken Fist. She could show him how to use his chakra more effectively while performing the drunken - like maneuvers.
A traveling nen master could be Naruto's mentor. This master could be on a journey to spread the knowledge of nen. He crosses paths with Naruto and decides to teach him. The master might have a strict teaching style, pushing Naruto to his limits, but also guiding him carefully through the complex world of nen.
There's a possibility that it's a spirit or a deity in the world of bending. This entity is impressed by Naruto's tenacity and chooses to guide him on his journey of learning bending.
Maybe Kakashi could still be his mentor. Even though One for All is a new and different power, Kakashi is very experienced. He could help Naruto understand how to incorporate this new power into his overall combat strategy. Kakashi would be able to analyze the power and give Naruto advice on how to train with it while still relying on his ninja skills.
There's a possibility that it's a spirit or a ghost of a past master of the drunken fist. Naruto somehow makes contact with this entity, and the spirit decides to pass on its knowledge to Naruto, guiding him through the process of mastering the drunken fist in a rather supernatural way.
Kakashi could be a great mentor. Since he was Minato's student, he has first - hand knowledge of Minato's techniques. He could teach Naruto the fundamentals of the Yellow Flash's fighting style, like how to control chakra for high - speed movement.
Maybe Tsunade could play a role in mentoring Naruto in Doton techniques. She has a vast knowledge of different jutsu, and it would be interesting to see her help Naruto develop his Doton skills, perhaps as part of a broader training regime to make him a more well - rounded ninja.