Perhaps a fallen god who, despite losing his status, still has the knowledge of how to train a God of Destruction. This character could have his own motives for training Naruto, like regaining his former glory through Naruto's success.
There's also the possibility that it's a mysterious figure that Naruto meets during one of his adventures. This trainer could be a shape - shifter, able to take on different forms to teach Naruto different aspects of destruction - related powers, like teaching him how to use destruction energy in combat in one form and how to control it in a more peaceful state in another form.
Maybe it's a member of a long - lost ninja clan. This clan member could have some special skills and knowledge that they want to pass on to Naruto. They choose to train him in secret to protect their clan's secrets from falling into the wrong hands.
In this fanfic, the plot could involve Naruto being taken to a special realm where the God of Destruction's training takes place. He would have to unlearn some of his ninja ways and adapt to new combat styles. There, he would face challenges that test his mental and physical limits, such as controlling destructive forces without causing too much chaos. He may also meet other powerful characters who either help or hinder his training.
It could be an unknown ninja from a far - off village who specializes in Storm Release. This ninja might have heard of Naruto's potential and decided to train him.
It could be an old, retired ninja who lives on the outskirts of the village. This person has seen the hardships Naruto faces and decides to take him under their wing.
Sasuke could be one of his allies. Despite their past differences, Sasuke would recognize the potential of Naruto's new power and the good it could do. Also, Kakashi could be an ally. His wisdom and experience would be valuable in guiding Naruto in this new role. And of course, the other members of the Konoha 11, like Sakura, who would support Naruto in his journey as a god of destruction, believing in his good intentions.
It could be Kakashi. He has a lot of knowledge and skills that he could pass on to Naruto more intensively. Maybe he takes Naruto on a long - term mission where they train on the go. Kakashi could focus on improving Naruto's Sharingan - like observational skills and help him develop new strategies for combat.
Kakashi could be another one. Since he's already Naruto's teacher in the original story, it's not a stretch to think he could start training Naruto even earlier in the fanfic. He could focus on different aspects of Naruto's abilities, like improving his stealth or his chakra control even more.
It could be a really wild and exciting concept. Naruto, with his new role as a God of Destruction, might have powers far beyond what we've seen in the original series. He could have the ability to level entire landscapes with a single thought. His character would likely undergo a significant transformation, perhaps becoming more aloof or having a different view on the world he once protected.
The plot could involve Naruto being chosen by some ancient prophecy to become a god of destruction. He first has to go through a series of trials. These trials could test his mental and physical strength as well as his understanding of power. Once he becomes a god of destruction, he has to balance his new role with his old ninja values. He might face challenges from other powerful beings who don't want a newcomer in the role. Naruto would then have to prove himself worthy by using his powers for justice and protection.
It could be a rogue ninja who has also harnessed the power of a god of destruction. This ninja wants to use the power to rule the ninja world and Naruto has to stop him.