One possible plot could be that Naruto is exposed to a very dark and powerful jutsu that corrupts his mind. This jutsu could be some ancient, forbidden technique that no one was aware of its full power. As it takes over his mind, Naruto's values change drastically. He begins to enjoy causing pain and chaos. He might use his skills not to protect but to dominate and instill fear in others, completely opposite to his original character.
His friends would be horrified. Sasuke, for instance, who has known Naruto for a long time, would be shocked at this transformation. He might initially try to reason with Naruto, thinking that there's still some good left in him. But as Naruto's psychopathic behavior continues, Sasuke would be forced to consider him an enemy and take action to stop him if necessary.
Maybe Naruto discovers Bakugan during one of his travels outside the Hidden Leaf Village. He could be intrigued by the unique powers and battles of Bakugan. He might start collecting them and use his ninja skills to master the Bakugan battles, making new friends in the Bakugan world who are also impressed by his ninja abilities.
One possibility could be that Naruto is somehow transported to a realm where he meets Thanoso. Maybe he has to learn Thanoso's special abilities to defeat a new, powerful enemy in his own world. He could start training under Thanoso and gradually adopt some of his characteristics in combat.
One possible plot could be that Naruto, always being competitive and seeking new challenges, discovers the world of racing. He might start by being in awe of the speed and skill of the racers. He then begins to train himself in racing techniques, using his ninja agility and quick - thinking. He could enter local races and gradually make a name for himself in the racing world, all while facing rivals who underestimate him because of his ninja background.
One possible plot could be that Naruto is exposed to a powerful and dark jutsu that slowly turns him into a demon. As he transforms, he has to struggle with his new nature. His friends initially fear him but then try to find a way to reverse the process.
One possible plot could be that Naruto is cursed by a powerful enemy. This curse transforms him into a wolf. As a wolf, he has to adapt to his new form. He might discover new abilities like enhanced speed and sense of smell. His friends initially don't recognize him and he has to find a way to communicate with them. Eventually, he goes on a journey to find a way to break the curse.
Well, perhaps Naruto discovers a new world of anthropomorphic animals and is intrigued. He might start to make friends with these furry characters and learn about their unique cultures.
One possible plot could be that Naruto is somehow cursed or transformed into a succubus. He might initially struggle with his new form, having to deal with new instincts and powers. For example, he could find himself having an unexpected allure that affects his friends and foes alike. He would then have to learn to control these new aspects of himself while still trying to protect the village and his loved ones.
One possible plot could be that Naruto, through some mysterious jutsu gone wrong, starts to take on aspects of Menma's personality. He might become more laid - back and carefree like Menma. This could lead to some interesting interactions with his friends. For example, Sasuke might be really confused at first, seeing Naruto so different. And Sakura might try to figure out what happened and how to bring the old Naruto back. The story could also explore how Naruto's new - found Menma - like qualities affect his ninja training and his relationships with the villagers.
In a 'naruto becomes a witcher fanfiction', Naruto would likely face challenges adapting to the Witcher world. He'd have to get used to the different types of monsters and the way magic works there. His Rasengan could potentially be modified into a Witcher - like power move. He may also encounter difficulties with the Witcher's code and ethics, as he has his own set of values from being a ninja. But in the end, he could become a great Witcher, respected for his unique abilities.