Perhaps Naruto meets a Sadaiam character who has a really kind heart and strong sense of justice, much like himself. This person shows Naruto the beauty of Sadaiam art, music, or philosophy. Naruto, being the open - minded person he is, gets immediately drawn to it. He might then start promoting Sadaiam values among his friends in Konoha, which could cause some interesting cultural exchanges and a few conflicts too as not everyone might be as receptive.
He might become more serene. Since Sadaiam might have a calmer and more nature - centered philosophy, Naruto could adopt some of that. He'd be less impulsive in his actions and more contemplative.
Another possibility is that he gets help from a powerful ally. This ally could be a sage or a spirit who bestows upon Naruto the power of invisibility. They might see Naruto's potential and the importance of his mission and decide to give him this special ability. It could also be a side - effect of a powerful transformation he undergoes, like a new sage mode or some other super - powered form that has the added benefit of making him invisible.
It's possible that an outside force from another country is behind it. They want to weaken the Land of Fire by putting Naruto, a powerful and unpredictable element, in a position where he has to deal with political matters rather than ninja battles. They believe this will make the Land of Fire more vulnerable to their future attacks.
It could be that after some great battle where the Hidden Rain is left in a state of chaos, Naruto steps in to help rebuild. His selfless actions during this time earn him the trust and respect of the Rain villagers, leading to him being named the Amekage. He might have used his Rasengan and Sage Mode skills to protect the village during the battle, which makes him a natural choice for leadership.
In a fanfiction, Naruto could become the Mizukage through various means. Maybe after some great diplomatic efforts between Konoha and the Hidden Mist Village. He could prove himself worthy by helping the Mist Village solve some internal problems like dealing with rogue ninja groups that the Mist has been struggling with. His skills in combat and leadership would also play a big role. He could train the Mist ninja in new jutsu and battle strategies, thus earning their respect and ultimately being named the Mizukage.
Well, Naruto is a complex character. Initially, he may feel a sense of confusion. He might wonder why he is being forced when he has his own ideas about what he wants to do. He could also feel a bit of fear, not really knowing what being a ninja fully entails. He might be worried about whether he can meet the expectations that come with this forced role.
In some fanfictions, Naruto becomes a legend by achieving feats even greater than in the original story. For example, he might master new and extremely powerful jutsu that no one has ever seen before. This could include a unique form of Rasengan that can destroy entire armies with a single blast.
In fanfiction, Naruto could become invincible if he had a unique genetic mutation. This mutation could enhance his already formidable Uzumaki bloodline powers to an extreme degree. His healing factor could become so powerful that he can recover from any injury instantly. His strength could increase to the point where he can shatter mountains with a single punch. Also, his speed could be enhanced to the level where he can move faster than the eye can see, making him practically invincible against most opponents.