One possibility could be that Naruto is drawn to boxing because of its physicality and the determination it requires. He might see it as a new way to test his strength and endurance outside of ninja battles. Maybe he starts training with a local boxing coach who sees his potential and helps him develop his skills.
Well, you might want to check out 'Harry's Double Life'. In this fanfic, Harry pretends to be a Muggle exchange student to investigate some mysterious events at Hogwarts.
Perhaps Naruto's transformation into a Predator - like being changes his appearance. He might have some Predator - like physical features such as glowing eyes or enhanced strength. This could lead to his friends initially being scared or confused, but as they see him use these new powers for good, they come to accept him. In the story, he could also learn to control these powers, so they don't overtake his original ninja nature.
One possible scenario in a fanfiction where Naruto becomes Pein could be that Naruto is exposed to some dark jutsu that alters his mind. This jutsu might be related to the Rinnegan's power. As a result, he starts to adopt Pein's ideology of bringing pain to the world in order to create peace. His friends would be shocked and try to bring him back to his normal self.
Well, Naruto as a genie would be a really cool idea for a fanfiction. His character already has a strong sense of justice and a big heart. As a genie, he would be able to spread his positive influence even more widely. Imagine Naruto granting the wish of a poor village for food and resources. He could also use his genie powers to create illusions on a grand scale, fooling the enemies of the village. And his bottle or lamp (where he is trapped as a genie) could be hidden in some super - secret location in the Hidden Leaf.
One possible scenario could be that Naruto is transported to the Flash's universe and somehow gains the powers of Savitar. He might use Savitar's speed in his own unique way, like combining it with his shadow clones to create a sort of blitzkrieg attack. Maybe he would also struggle with the darker aspects of Savitar's power, as Naruto is typically a more positive - minded character.
The theme of acceptance is also prevalent. Juvia may have to accept her new feelings, even if they go against what others expect of her or what she expected of herself. And she also has to deal with the acceptance or rejection from the person she loves, which can be a very emotional journey in these fanfictions.
His friends like Sasuke, Sakura, and Kakashi would surely support him. They have been through a lot together and know Naruto's good heart and leadership potential.