If Naruto is a Madara fan in the fanfiction, his character development could take a darker turn. He might be influenced by Madara's power - hungry side and start to become more ambitious in a negative way. However, it's also possible that he would take the good parts of Madara, like his determination, and use it to fuel his own positive growth, while still maintaining his core values of friendship and peace.
Naruto might become more conflicted. Since Madara had some extreme views, Naruto would have to grapple with those ideas. He could become more secretive as he tries to understand Madara's motives better without alarming his friends. For instance, he might start training alone more often to study Madara - inspired techniques.
Naruto would likely become more serious. Madara's influence would probably make him less impulsive. For instance, he would think twice before charging into battle without a proper plan.
In this fanfiction, Naruto's character development could be seen as a counterpoint to Madara's. Naruto is all about hope, friendship, and protecting the village. Madara has been through a lot of pain and betrayal which led him to a path of destruction. If Naruto is like Madara in this fanfiction, his development might involve a struggle between his own beliefs and the allure of Madara - like power and ruthlessness. However, Naruto would probably still find a way to use any new - found power in a more benevolent way compared to Madara.
The OC would likely start as a relatively inexperienced ninja. Under Madara's tutelage, they would become more confident and skilled. For example, they might learn how to better control their chakra.
Naruto being raised by Sasori would be a huge shift. Sasori is not one to show much emotion or promote the ideals of hope and perseverance like the people in Konoha. Naruto would likely have a different sense of loyalty, perhaps more towards Sasori's goals or ideals which are mainly centered around his own power and the art of puppetry. His growth as a ninja would be more focused on silent and deadly skills rather than being a hero that everyone looks up to. His relationships would be more transactional in nature as he wouldn't have been exposed to the deep emotional bonds that are so prevalent in Konoha.
If Naruto was raised by Vegeta, his character would likely become much more aggressive and focused on power. Vegeta's Saiyan pride and his constant drive to be the strongest would rub off on Naruto. He might not be as friendly or as empathetic as in the original series, but would instead be more solitary in his pursuit of strength, seeing it as the ultimate goal.
It would likely accelerate his growth. Jiraiya is a very experienced ninja. With his guidance, Naruto would gain more confidence. For example, if Jiraiya found Naruto early on, he could teach Naruto better control of his chakra, which was a struggle for Naruto in the beginning. This would make Naruto more efficient in battles and less reliant on brute force.
Naruto would likely become more disciplined. Kakashi is known for his strictness, so Naruto would have to follow a more structured training regime. This would make him more focused during battles and in his studies of ninjutsu.
Naruto would become more well - rounded. With Hiruzen's training, he'd gain more discipline. In the original, Naruto was a bit of a wild card. But under Hiruzen, he'd learn to control his impulses better. For example, in battles, he'd think more strategically instead of just charging in.
Well, when Madara gives Naruto his Sharingan in the fanfiction, Naruto's character development would take a very interesting turn. He has always been about his own unique brand of ninja way, which is based on hard work, friendship, and never giving up. With the Sharingan, he'd have to balance this new power with his existing values. He might face temptations to use the Sharingan for shortcuts or for revenge if he ever faced enemies related to the Uchiha's past. However, I think Naruto would ultimately use it in a way that aligns with his positive nature, perhaps to protect his friends and the village even better. But the internal struggle and the growth he'd experience while learning to control and use the Sharingan would be a significant part of his character development.
The story would change drastically. Naruto's identity as a descendant of Madara would immediately put him at odds with some in the village who still fear the Uchiha. His journey to become Hokage would be even more challenging as he has to prove that he's not going to follow in Madara's footsteps. Also, his training might take a different route. He could be taught some ancient Uchiha techniques by an unexpected mentor, perhaps an old Uchiha who has been in hiding.