One possible motivation could be a sense of betrayal. If he discovers that the village leaders had been using him all along, he might turn bad. Another could be the loss of someone dear to him in a way that he blames the ninja world for. So, he decides to take revenge on it.
If Naruto becomes a bad guy in a fanfic, it would completely shatter the original story's foundation. His friends like Sasuke and Sakura would be forced to oppose him. The village that once saw him as a hero would now view him as a threat. All the bonds he had built throughout the series would be put to the test. His transformation could lead to new alliances and rivalries, for example, he might team up with the villains from the original story, creating a whole new power dynamic.
Sakura would be shocked and heartbroken. She has always seen Naruto as a positive force. She would try to understand what led Naruto to this change and might attempt to use her medical ninjutsu to see if there's some sort of mental or physical ailment causing it. And she would definitely be among the first to oppose Naruto if he starts doing harmful things.
There could be a group of orphaned ninja - in - training that Naruto takes under his wing. These students would look up to him not only as a teacher but also as a symbol of hope, much like how Naruto once looked up to Iruka - sensei. They could come from various backgrounds and clans, and Naruto would have to find ways to bring out the best in each of them.
In a fanfic where Naruto is a pervert, his training and growth would likely take a backseat. Instead of focusing on becoming stronger and protecting the village, he might be preoccupied with inappropriate things. This would not only affect his own character development but also the development of the story as a whole. The fanfic would probably lose the essence of what makes Naruto so great, which is his journey of self - discovery, his will to overcome difficulties, and his ability to inspire others. It would be a rather dark and unappealing take on the character.
One common motivation is the pursuit of power. In Naruto fanfic, characters might be driven to become stronger to protect their village, like Naruto himself. Another motivation could be revenge. For example, a character whose family was killed by a certain villain in the Naruto universe might be motivated by revenge in the fanfic. Also, love can be a strong motivation. A character could be motivated to achieve great things to win the heart of their beloved.
Shikamaru, being the intelligent one, would try to analyze the situation first. He would understand that Naruto isn't himself and would start to plan a way to reverse whatever happened. He might try to gather the other ninja to form a strategy. Kakashi would be deeply disappointed. He has trained Naruto and seen his growth, and this change would be like all his efforts going to waste. He would try to talk to Naruto, using their past experiences to try and break through to the real Naruto inside.
His relationship with Sakura would change a lot. Sakura might be more protective of Naruto as a cat, seeing him as a cute and vulnerable creature. She might take on a more motherly role towards him. With Kakashi, Kakashi would probably be amused by Naruto's cat form at first, but then he'd start to worry about how to turn him back. And as for his friends in general, they'd have to communicate with him in different ways, like through body language and meows.
His relationship with Sasuke would be greatly affected. Sasuke might see Naruto as a completely different person now that he has become the Nine - Tails. There could be a sense of fear or at least a new level of caution from Sasuke. They might have to re - establish their bond, as Naruto's new form could be a threat in Sasuke's eyes.
Naruto's personality would change in several ways. He would become more aggressive, which is a big part of Wolverine's character. He might be quicker to anger and less patient. However, he would also have a sense of loyalty like Wolverine. His old self - sacrificing nature would still be there but it would be expressed in a more Wolverine - like way, being more protective and ready to fight for those he cares about without hesitation.
Naruto's relationship with the younger generation would be very different. As a Jounin, he would be a role model. The kids in the village would look up to him even more. He could inspire them to work hard. His relationship with Hinata might also evolve. Maybe he would finally have more time to focus on their relationship now that he has achieved a higher rank and more stability in his ninja career.