An older, more experienced ninja from a hidden village that specializes in needle - based jutsu could become his mentor. This ninja could have unique insights into the art of using needles, teaching Naruto different formations and strategies for using them in battle.
It could be an old hermit living in the forest who has a deep connection with nature and Mokuton. This hermit has been observing Naruto from afar and decides to come forward to teach him. The hermit could have a different approach to using Mokuton, one that is more in tune with nature's balance, which Naruto would find both challenging and enlightening.
Perhaps the Sage of Six Paths could be his mentor. Since the Sage has great knowledge and power, he could guide Naruto in understanding and using soul magic. Another option could be Jiraiya. Even in death, Jiraiya's spirit could communicate with Naruto and teach him about soul magic through visions or dreams.
Dumbledore could also be his mentor. Dumbledore was knowledgeable about many things, and it's possible that he had some understanding of alchemy. He could encourage Harry to explore alchemy as a way to enhance his magical abilities and use it for good.
Sasuke could be Naruto's parkour mentor. Despite their past differences, Sasuke has great skills in movement and agility. He could teach Naruto more refined parkour techniques, like how to land more quietly or how to make sharper turns while running on rooftops.
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.
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.
Even an older Uchiha like Itachi (in a non - villainous AU perhaps) could be a mentor. The Uchiha are known for their fire - based jutsu. Itachi could teach Naruto the subtleties of fire control, like how to vary the intensity and shape of the flames for different combat situations.
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.
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.