Perhaps it's about Naruto being transported to the Dark Carnival universe and having to team up with some of the characters from that world to stop an even greater evil. He could bring his values of friendship and perseverance to the new setting, which would contrast with the more dark and twisted nature of the Dark Carnival.
Yes, there are likely fanfictions out there with that concept. Fanfiction writers often create unique crossovers, and combining Naruto with the Dark Carnival universe is a creative idea that someone may have explored.
Another idea is that Naruto has a dark secret regarding his past training. Maybe he had to do some unethical or dangerous things during his training with Jiraiya that he's ashamed of. This could include using forbidden jutsu or making deals with dark entities in order to gain power, which would be a huge shock to his friends and the village if it ever came out.
A plot could revolve around a dark force corrupting both Naruto and Hinata. This force might be an ancient evil that has been dormant for years. As Dark Naruto and Dark Hinata, they might target their former friends. Naruto could use his shadow clones in more menacing ways, and Hinata could use her Gentle Fist techniques to cause harm instead of protect. They could form an alliance with other outcasts or villains in the Naruto universe.
One possible plot could be that Dark Naruto, who has turned to the dark side perhaps due to being ostracized or some great tragedy. Ayame, on the other hand, tries to reach out to him. She might believe in the good that still exists within him. She could start by bringing him food from her family's ramen shop, as food has always been a connection between Naruto and the village. Through these small interactions, Dark Naruto might start to question his new dark path, and slowly, a relationship could develop between them where Ayame is the light trying to bring him back from the darkness.
Well, it might be about how Naruto's life changes with the ketsuryugan. He could face new enemies who are interested in this new power he has. Also, his friends might react in different ways, some being worried and some being excited. And he could use the ketsuryugan to unlock new jutsu or abilities that are related to it. He might also have to deal with the origin of the ketsuryugan and any secrets that come with it. This could lead to a whole new adventure for Naruto, exploring new places and meeting new characters in the process.
It could be about Naruto finding a Teigu during one of his adventures. Maybe he discovers it in a hidden place and has to figure out how to use it to fight his enemies in the Naruto world.
It could be about Naruto obtaining a Persona. Maybe during one of his adventures, he stumbles upon a strange power that turns out to be a Persona. He then has to learn how to control it while still using his ninja skills.
I'm not entirely sure specifically as there could be many different 'dark fanfictions' related to Naruto. Generally, it might involve darker themes such as exploring the characters' inner demons, darker versions of the ninja world, or alternative and often more tragic storylines compared to the original Naruto series.
Well, it could be that Dark Naruto, after being abandoned, is found by an outcast group. They take him in and teach him their own values which are different from the village's. He grows up with a different perspective and starts to question the whole idea of the ninja world. Eventually, he might try to create his own 'utopia' in his mind, which could involve overthrowing the current system. But at the same time, he still has that internal conflict of his Uzumaki heritage and what Kushina's abandonment means.
Well, in this fanfiction, the story might start with Dark Naruto being on a rampage. Fem Haku, being a skilled ninja in her own right, decides to face him. But as she gets closer, she realizes that his darkness is born out of pain and loneliness. So, instead of fighting, she offers him an alternative path. This could lead to a series of adventures where they both learn from each other and grow. For example, Haku could teach Naruto about self - control and Naruto could teach Haku about the power of determination.