Rock Lee could be a really unexpected but fun main character. He's always looking for challenges, and getting involved with a crime boss could be the ultimate test for him. He could be trying to reform the crime boss with his positive attitude and unwavering ninja way, or he could be tricked into working for the crime boss at first and then has to find a way out.
Sasuke could be a great choice. He has that brooding, anti - hero vibe that could fit well in the criminal underworld. Maybe he gets drawn into the crime boss's schemes because he thinks it's a way to gain more power to achieve his own goals.
It could be an old veteran ninja who, after years of service, decided to open a shop. He has a gruff exterior but a heart of gold. He uses his war stories to attract customers, especially the young ninja trainees who are eager to hear tales from the front lines while they browse his selection of kunai and shuriken.
Well, perhaps the crime boss in the fanfic is in cahoots with some of the hidden villages' enemies. He could be smuggling dangerous weapons or forbidden jutsus across the ninja world. He might also be using his charm and intelligence to recruit other ninjas to his side, promising them power and wealth. He could have a network of informants in every village, which makes it really difficult for the good guys to track him down.
In some 'naruto multiwives fanfic', Hinata is often a potential wife for Naruto. Given their relationship in the original series, it's easy to imagine her as one of his wives. Sakura could also be a candidate. Even though her feelings were mainly towards Sasuke in the original, in fanfic, things can be different. And then there's Ino. She has her own charm and abilities, and could be one of Naruto's wives in the fanfic world.
Kakashi could still be an important ally even though Naruto has become a Jounin. Kakashi has a wealth of experience and knowledge that Naruto could still learn from. He could offer advice and assistance when Naruto faces tough challenges in his new role.
Hanabi could become more confident. With Naruto's training, she might start believing in her abilities more. For example, if Naruto encourages her during tough training sessions, she'll feel more self - assured in her skills.
Ruby could be a potential ally. She is brave and has a strong sense of justice, just like Naruto. They could team up and use their unique abilities to fight against the Grimm. Another one could be Jaune. He is a bit of an underdog, and Naruto has a soft spot for those kinds of characters. He could help Jaune improve his skills.
A likely main character could be a young ninja who discovers he has the 'One for All' power. He would be on a journey to understand and control it, while also dealing with the normal challenges of being a ninja in the Naruto world, like training and making friends.
Naruto himself could also be a main character. He could visit the Hidden Star Village and interact with the Hoshikage, getting involved in the village's affairs and helping them solve their problems. This would be an interesting way to incorporate the Naruto we all know into the fanfic.
At first, Naruto might become more secretive. He'd be hiding his new 'profession' from his friends, which is very different from his usual open - natured self. This could cause some internal conflict as he doesn't like lying to them.
Power and control are common themes. As a crime boss, Naruto would be seeking to gain and maintain power over his criminal empire. Another theme is loyalty, or lack thereof. Who can he trust in this new world of crime? Also, revenge might be a theme if his turn to crime is due to some wrong done to him.