Maybe the plot could revolve around Naruto getting influenced by a powerful and evil entity. This entity could corrupt his mind, making him believe that the only way to achieve true peace is through domination. So, he would begin to gather power, using his skills and charisma, but for the wrong reasons. He would form his own group of followers, who also believe in his new 'world order' ideas, and start a war against the existing shinobi villages.
If Naruto loses all his friends in a tragic way, perhaps in a battle against an overwhelming enemy that the village could have prevented. His grief could turn into hatred towards the shinobi system. He may decide that the existing order is what causes all this pain and destruction, and then he starts to work against it, becoming a villain in the eyes of the village.
His confidence could turn into over - confidence bordering on arrogance. As a villain, he might think he is above everyone else and that his way is the only right way. He would no longer listen to advice or consider the consequences of his actions on others, believing that he can handle any situation on his own, no matter how dangerous or unethical.
It could be Kabuto. Since he has a lot of knowledge about medical ninjutsu and experiments, he might see Naruto's robotic form as a threat or something he can use for his own evil purposes. He could try to control Naruto's robotic functions and turn him against his friends.
If Naruto turns into a super villain in fanfiction, perhaps his transformation is due to some dark influence. It could be a powerful and evil chakra that corrupts him. He would then start to use his jutsu in cruel and unexpected ways. For example, instead of using the Rasengan to protect, he might use it to destroy important buildings or harm innocent people. His friends would be shocked and try to bring him back to the good side, but he would be too far gone. This could lead to some really intense battles and emotional confrontations between him and his former comrades.
There were a few novels that traveled across the universe and became villains, including " The Great Villain: Let the Female Lead Save Me in the Finale,"" I Am a Villain in the Movie World,"" I Am a Villain in the Universe,"" I Am a Big Boss in the Universe,"" The Days of Being a Villain in the Universe,"" The Villain Chat Group in the Universe,"" The Counterattack of the Villains in the Universe,"" Crossing the Universe as a Villain,"" The Great Villain in the Universe," and so on. These novels covered different topics and storylines, and readers could choose to read them according to their interests.
One possibility could be that Batman, after facing one too many betrayals in Gotham, decides to take a different path. Maybe the constant struggle against crime with little real change in the city makes him cynical. He could start using his skills and resources to control the underworld instead of fighting it. For example, he might start dictating which criminals can operate and where, creating a new order that is still dark but under his command.
Most Naruto fanfics tend to focus on his adventures, his relationships in a positive way, like his bond with Sasuke or his training with Kakashi. The idea of Naruto becoming a pervert is quite out of the ordinary for the Naruto - themed fanfic world. It's not something that is typically explored in mainstream Naruto fan creations.
If Naruto becomes a villain in the DC crossover, he might set his sights on Superman. Naruto could believe that Superman's power is a threat to the balance he wants to create. He would use his ninjutsu to try and take on Superman. For example, he could use his Rasengan, a powerful spinning ball of chakra. However, Superman's strength and heat vision would be tough for Naruto to overcome. This would lead to an epic battle between the two, with the other DC heroes and Naruto's possible allies getting involved as well.
First, decide on their backstory. Maybe they had a rough childhood in one of the hidden villages that led them to turn bad. For example, if they were from the Hidden Leaf, they could have been shunned for not having strong ninja skills initially. Then, design their appearance. They might have a unique hair color or style, like long white hair to give an air of mystery. Also, think about their abilities. It could be a special jutsu related to shadows or something that's not commonly seen in the Naruto world.