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.
Characters like Kakashi would be deeply concerned. Kakashi has known Naruto for a long time and has seen his growth. To see Naruto acting like Madara would make him wonder if there's some external influence or if Naruto has lost his way. He might try to use his own experiences and wisdom to guide Naruto back. And villains in the Naruto world might see this new Naruto as either an opportunity to team up with him if they think he's truly turned dark, or they might be wary of him if they think he's still got some of his old self and could turn against them.
Sakura would be worried sick. She'd try to figure out what happened to Naruto to make him act this way. She might try to talk to him, use her medical ninjutsu to check if he's under some kind of genjutsu or has some other problem. She'd be very vocal about her concerns and would try to get the other villagers to help bring Naruto back to his normal self.
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.
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.
His friends' reactions would be quite diverse. Kakashi, for example, might be intrigued by Naruto's new behavior. He could see potential in Naruto's new - found Kisuke - like qualities. The younger generation of ninja, like Boruto if he were around in this scenario, would look up to this new version of Naruto even more. They'd be inspired by his new cool - headedness and intelligence, while also being a bit in awe of his sudden change in demeanor.
If Naruto acts like Madara in the fanfic, he may begin to view the ninja world in a more cynical way. He could start to question the current system of peace and might try to reshape it according to his own vision, which would lead to battles with those who oppose him. Also, his relationships with characters like Sasuke would take a new turn, perhaps becoming more of a rivalry based on different ideologies.
The fanfiction could explore Naruto being in a situation where he has to act like Madara to deceive the enemy. He gradually gets too deep into the role and starts to actually think and act like Madara on a more permanent basis. His friends notice the changes in his personality, like his increased aggression and his new - found belief in power as the ultimate factor in achieving goals. They then try to bring the old Naruto back.
For Hinata, it would be a crushing blow. She loved Naruto so much. She might withdraw into herself at first, overcome with grief. But then, she could find the strength within herself to carry on Naruto's legacy, especially for their son, Boruto (if in a post - Naruto - has - a - family scenario in the fanfiction). Shikamaru, being Naruto's friend, would feel a deep sense of loss. He would use his intelligence to try to figure out what led to Naruto's death and if there was any way to prevent it in hindsight. And the other members of the Leaf Village would be in a state of shock and mourning. Naruto was their hero, and his death would make them question their safety and future without him.
If Naruto was an Ajin in a fanfiction, the characters in Naruto would have a mix of reactions. Hinata would be concerned for Naruto's well - being. She might be a bit scared at first because of his new and strange abilities, but still stand by him. The villagers, who have had a rocky relationship with Naruto in the past, might be afraid of him all over again. They could see his Ajin powers as a threat. On the other hand, Naruto's close friends like Shikamaru would try to understand what's going on and help Naruto control his powers if they can.
Sasuke might be conflicted. He has his own complex relationship with Naruto. Part of him might understand Naruto's reasons for leaving, but he could also be angry that Naruto didn't confide in him. Sakura would be worried sick. She has always cared about Naruto, and his leaving would leave a big hole in the team. Kakashi, on the other hand, would be disappointed but also respect Naruto's decision if he thought it was for a noble cause.
Iruka - sensei would be very concerned. He's always been like a father figure to Naruto. He'd probably spend a lot of time with Naruto, sharing stories from Naruto's past when he was brave and encouraging him to find that courage again. Kakashi - sensei would be more analytical. He'd observe Naruto closely, trying to figure out if this is a mental block or something more sinister. And the other villagers might start to lose faith in Naruto as their hero, which would add more pressure on Naruto to overcome his fears.