In this fanfiction, Naruto will surely interact with his friends who might be trying to break him out or at least communicate with him from the outside. Inside the prison, he'll encounter inmates with diverse personalities. There could be a wise old prisoner who imparts some valuable wisdom to Naruto. Also, there may be a group of inmates who form a sort of gang within the prison, and Naruto has to either fight them or make peace with them depending on the situation. And of course, there could be a mysterious figure who seems to know more about Naruto's presence in the prison than he himself does, and Naruto will have to figure out this person's motives and identity.
He would likely interact with the Dragonborn. They could have an interesting exchange of skills, with Naruto showing off his Rasengan and the Dragonborn demonstrating shouts. He might also meet the various Jarls in the different holds, trying to understand their leadership styles which are different from the Hokage in Konoha.
Obviously, Koyuki herself would be a main character to interact with Naruto. She might show him around her place, introduce him to her people. Also, any of her loyal guards or advisors could interact with Naruto. They could be initially suspicious of him but then grow to trust him as they see his good intentions.
Iron Man is another candidate. Tony Stark's technology and Naruto's ninja techniques could be a great contrast. They could learn from each other. Stark might be interested in Naruto's chakra - based powers and try to replicate them in some way, while Naruto could be amazed by Stark's high - tech gadgets.
Kakashi could also play a role. He has been Naruto's mentor for a long time. So, he might have some mixed feelings about Itachi adopting Naruto. He could be suspicious of Itachi's motives at first but then gradually come to understand Itachi's positive influence on Naruto. Their interactions could be really fun to read about, especially when Kakashi tries to give Itachi some advice on how to handle Naruto's wild nature.
Rukia might also interact with Naruto. She's kind - hearted and might see Naruto's potential. She could be the one to first notice Naruto's situation and try to bridge the gap between him and the rest of the Soul Society. For instance, she could introduce Naruto to some of the more open - minded Soul Reapers.
Obviously, Nagato himself would be the main character interacting with Naruto. He would be like a mentor or a guardian figure in Naruto's life.
Definitely the Teen Titans. Robin would be interested in Naruto's strategic mind and combat skills. Starfire might be fascinated by Naruto's unique culture. Beast Boy and Naruto could bond over their fun - loving natures. And Cyborg would be intrigued by Naruto's chakra - based abilities compared to his technological ones.
Well, Lucy would be likely to interact with Naruto. She's friendly and curious, so she'd probably be one of the first to approach Naruto and try to understand where he came from. Gray is also a candidate. His cool - headedness (pun intended) would contrast with Naruto's more energetic personality. And of course, Makarov, the guild master. He would be interested in Naruto's abilities and might offer him a place in the guild or give him some tasks to prove himself in the Fairy Tail world.
Anko might also be involved in the story. She has her own unique relationship with Yugao and could potentially interact with Naruto. Maybe she gives Naruto some tough love or challenges him in a way that Yugao's teaching methods don't cover. And of course, Iruka sensei could also show up to check on Naruto's progress and have some interactions with both Naruto and Yugao.
Definitely Naruto and the Punisher first. Naruto would be intrigued by the Punisher's methods and would try to understand his motives. It's also possible that Sakura could interact with the Punisher. She's a strong - willed character, and she might try to either stop the Punisher if she thinks his actions are too extreme or help him if she sees the good in his goals. And Jiraiya might also be a character who could cross paths with the Punisher. Jiraiya's worldliness and his own sense of right and wrong could lead to some deep discussions between them.