Sasuke could be one of the main characters to interact with Dark Naruto. Given their complex relationship in the original Naruto series, Sasuke might be either drawn to help Dark Naruto because of their shared past, or he could see Dark Naruto as a threat to his own goals and power. They could have some intense battles or deep conversations about the nature of power and the path they've both chosen.
Sakura is another potential character. She has always cared about Naruto in the original story. In the fanfiction, she could be torn between her loyalty to the old Naruto and her fear of the new, dark Naruto. She might try to use her medical ninjutsu to find a way to heal Naruto of his dark state, or she could be a voice of reason in the chaos that Dark Naruto brings to the village.
One idea could be exploring Dark Naruto's internal struggle. Maybe he's constantly fighting against the dark chakra within him and how that affects his relationships with the other characters in the Naruto universe. He could be on a journey to find a way to control or purge the darkness without losing his identity.
Naruto would likely be very curious about the Dark Souls world. He'd approach new characters with his friendly and open - minded nature. The more stoic Dark Souls characters might be initially confused by his exuberance. For example, he might try to befriend a knight from Dark Souls, who at first is wary but then comes to respect Naruto's strength. Sakura could use her medical ninjutsu to help injured Dark Souls characters, which would earn her their trust and loyalty.
In fanfictions, their interaction can be complex. Dark Naruto might be initially distrustful of Mikoto, seeing her as part of the system that failed him. But Mikoto, with her kind heart, tries to reach out to him.
Tsunade would definitely be one. As the most renowned medical ninja in the village, she could either be Naruto's mentor or a colleague. They could exchange medical knowledge and experiences.
In 'naruto as a cat fanfiction', Jiraiya could be an interesting character to interact with Naruto as a cat. He might see some potential in this cat - form Naruto for some new ninja techniques. The Akatsuki members could also interact with Naruto as a cat. For example, Itachi might sense something unusual about this cat when he passes through the village. And Konohamaru could be another character. He would be really excited to have a cool cat friend, not knowing it's Naruto.
Naruto might interact with Eostia's warriors. They could train together, Naruto showing them his ninja combat skills and them teaching him about Eostia - style combat. There could also be some mysterious characters in Eostia, like an old hermit who has some knowledge about Naruto's sudden appearance in their world and could guide him on his journey in Eostia.
Maybe a group of villains in the RWBY fanfiction are trying to summon Dark Naruto to use his power for their own evil purposes. The RWBY heroes find out about this plan and have to stop the summoning. Along the way, they meet some characters from the Naruto universe who are also trying to prevent the misuse of Dark Naruto's power.
One potential ally could be Neji. Neji has his Byakugan and his skills in combat. He could see the dark swordsman as an equal in terms of combat ability and form an alliance. Also, Tenten, who is fascinated with weapons. The dark swordsman's sword and his skills with it could draw Tenten's interest, and she might become an ally. They could exchange knowledge about different weapons and fighting techniques.
Definitely Sasuke. Their relationship is always a key factor. He could be a reluctant ally, or he might think Naruto's dark side is leading him astray in the rebuilding efforts. Then there's Kakashi. His wisdom and experience could be valuable to Naruto. And Hinata. Her love for Naruto might make her a strong supporter, and she could also use her Byakugan abilities to help in various ways during the rebuilding, like scouting for resources or potential threats.
The interactions would be complex. Naruto's dark smartness could make him more withdrawn, which would worry Ino. She might try to cheer him up or get him to open up, but Naruto would be less receptive. Shikamaru would be the one to approach Naruto on a more intellectual level. He might engage Naruto in discussions about the nature of power and morality. Ino would then chime in with her own emotional perspective, creating a triangle of different viewpoints and interactions within the story.