Sasuke would be very cautious. He has a history with Madara and would be on guard. He might not trust Madara even if Naruto believes in him.
The other ninja villages would be on high alert. Madara was a major threat before, and his revival would be a cause for concern. They might see Naruto's association with him as a dangerous move. However, some of the younger ninjas might be in awe of Madara's power and look up to Naruto for being able to handle the situation.
The Akatsuki members, if any are still around, would have mixed reactions. Some might see Madara's revival as an opportunity to further their own goals, while others might be worried that Madara would take over the organization again. And for Naruto's friends like Shikamaru, they would be worried about Naruto getting in over his head but also trust that he has a plan to deal with Madara.
Well, it could involve Madara having a new purpose. Maybe he decides to help Naruto against a new, greater threat. Since he was revived, he might have a different perspective on the ninja world now.
Sasuke would probably be one of the most affected. He might feel a mix of guilt for not being able to prevent Naruto's death in the first place and relief at his revival. Sakura would be overjoyed, and she'd likely be the first to rush to Naruto's side to check if he's really okay. Kakashi, on the other hand, would be more reserved in his reaction, but still happy to see Naruto back.
The other Konoha ninjas would be quite shocked. The Hokage, whoever it is at that time, would see Naruto's change as a potential threat to the village's stability. They would likely keep a close eye on him and try to figure out what caused this transformation. Meanwhile, the younger generation of ninjas who looked up to Naruto would be confused and disappointed. They expected Naruto to be their role model of a kind - hearted and positive ninja, not someone acting like the feared Madara.
Sasuke might be a bit taken aback at first. He's used to Naruto's normal look, and this change could make Sasuke see Naruto in a new light, perhaps as a more formidable opponent or an even stranger ally. Sakura would probably be shocked too. She might tease Naruto about it at first but then grow to accept it. Kakashi would likely raise an eyebrow and make a comment about how Naruto is always full of surprises with his new look.
It would depend on the writer's intention. If the focus is on Naruto's growth, he could start exploring new jutsu or forms of chakra control. Since he was revived by Madara, there might be some dark elements associated with his revival that he has to overcome. Maybe he has to fight off some sort of curse that came with the revival process. And he would have to do this while still trying to protect the people he cares about.
Obviously, Naruto himself is a main character as the story revolves around his revival. His friends like Sasuke, Sakura, and Kakashi are also likely to be main characters. They would be involved in the process of bringing Naruto back or in helping him adjust to his new life after revival.
Naruto would be extremely enraged. He would vow to rescue Sakura no matter what. He would immediately start gathering his friends and form a rescue team. Sasuke, on the other hand, might initially seem more reserved but would also be determined to get Sakura back. He would use his Sharingan skills to track Madara.
Naruto is often paired with Madara in some fanfictions. Their interactions can be really intense, as Naruto tries to either convince Madara to change his ways or fight against his reborn form.
Harry would be on guard at first. He has faced many dark threats in his life, and Madara would seem like another one. But as he gets to know Madara better, he might see some similarities in their struggles. Dumbledore would likely be very interested in Madara. He would try to understand Madara's motives and see if he could be an ally or a threat to the wizarding world. Dumbledore would be cautious but also open - minded in dealing with this new and strange character.
Sasuke is often a popular character in these fanfictions. He might play a role in helping Naruto against Madara or have his own motives during their battle. Kakashi can also be a prominent figure, perhaps using his Sharingan in a crucial moment to assist Naruto. Another popular character could be Hashirama, as his connection to Madara is a key part of the original story and can be further explored in fanfiction.