Definitely Shikamaru's friends like Choji. Naruto in Shikamaru's body would still have that bond with Choji, but it would be different. They might have conversations about food and friendship in a new light. Also, Ino would be a major character to interact with. Their relationship could change as Naruto is now in Shikamaru's body.
The Hokage, whether it's Tsunade or later Naruto's own self in the original timeline, would be someone he interacts with. Naruto might give different advice or offer new perspectives while in Shikamaru's body. And Kakashi too. Kakashi could notice the change in 'Shikamaru' and there could be some interesting exchanges between them.
The Akatsuki members could also be characters he interacts with. Naruto, in Shikamaru's body, would have to use his wits to deal with them. He might come up with new strategies to fight or avoid them, and there could be some tense and exciting interactions as a result.
Obviously, Sasuke would still be a major character she interacts with. Their relationship could be even more complex now that Naruto is a girl. Sakura might also have a different dynamic with Naruto. Instead of seeing her as a rival for Sasuke's attention, they could become closer friends and train together more often.
Obviously, the oc reborn as Issei would interact with Rias Gremory. She is a central character in the High School DxD world and as Issei is part of her peerage, the oc in Issei's place would have a lot of interaction with her. This could range from her guiding the oc in the ways of the devils to them having some sort of romantic or at least a very close friendship relationship.
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.
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.
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.
Obviously Naruto and Naruko will interact a lot. But also, characters like Iruka sensei might play a role. Iruka was important in Naruto's life, and he could also be a positive influence on Naruko. And Naruto's friends like Shikamaru, Choji, and Ino might interact with Naruko as well. They could be like her aunts and uncles, teaching her different things and having fun with her.
Issei would be a likely character for Evil Naruto to interact with. They could be either rivals or allies depending on the plot. Rias, as a powerful devil, would also cross paths with him. Her leadership and power would make for an interesting dynamic with Evil Naruto. And Akeno, with her mysterious nature, might also get involved in the story and interact with him in various ways.
Obviously, Naruto and Erza would interact a great deal. Naruto would also probably interact with Erza's friends from Fairy Tail. He might meet Natsu and they could have some interesting battles or friendly competitions. He could also interact with Lucy, and perhaps learn about celestial spirits from her.
The Raikage, Ay, would also interact with Naruto. He might be hesitant at first about Killer Bee adopting Naruto, worried about potential problems. But as Naruto shows his strength and loyalty, Ay could start to see Naruto as an asset to the village. And of course, Naruto's friends from the Hidden Leaf Village might come to visit or have some sort of communication with him, like Sakura and Shikamaru. They could be worried about Naruto living in a different village but also be proud of his new experiences.
Sasuke would definitely be one of the main characters to interact with Naruto. Their relationship has always been complex, and with Naruto as a girl, it could become even more so. Sakura would also interact a lot. She might be both jealous and intrigued by Naruto's new form. Kakashi too, as Naruto's mentor, would have to adjust to this change and guide 'her' in a different way perhaps.