In addition to the obvious ones like Naruto and Sakura, other characters from Sasuke's clan might interact with him. For instance, if there are any remaining Uchiha members, they might have mixed reactions. Some could be shocked and try to figure out what happened, while others might be more accepting. Also, characters like Shikamaru, who is very observant, would surely notice the change in Sasuke and might have some unique interactions, perhaps trying to figure out how this change could affect their team dynamics or the overall situation in the village.
Among the students, Hermione Granger - if we consider a scenario where this fanfiction has some sort of time - travel or alternate universe aspect - could interact with Severus. Hermione would be curious about Severus as a girl and might try to learn from her knowledge of potions. And Severus, in turn, could be both annoyed and impressed by Hermione's eagerness and intelligence.
Well, perhaps a plotline could involve Sasuke turning into a girl and using this new form to his advantage in some undercover mission. He could infiltrate an enemy group more easily as a girl. Also, there could be a love triangle where some of the characters who previously saw Sasuke as a male now have different feelings towards him as a girl, which would create a lot of drama and conflict.
Sakura also often appears. She might be confused by the changed behavior of the reincarnated Sasuke. Maybe the reincarnated Sasuke is more open and friendly towards her than the original Sasuke, which would lead to different interactions between them.
Well, obviously Naruto and Sasuke are the main ones. Since it's about Naruto absorbing Sasuke, their relationship is at the core. But also, characters like Kakashi could be involved. He might be the one guiding Naruto on how to control his new powers or trying to understand the implications of this strange occurrence.
The main characters Damon and Bella will interact with each other on multiple levels. Damon will probably teach Bella about the vampire way of life. There could be other vampires from different clans that cross their path. These vampires might be curious about Bella or have their own agendas. Additionally, if the fanfiction has a touch of the supernatural world at large, angels or demons (if they exist in that universe) could also interact with them, adding a whole new layer of complexity to the story.
Obviously, Naruto and Sasuke are the main characters. Naruto is the one on the mission to retrieve Sasuke, so he will be at the forefront of the story.
There could be Naruto. Since he and Sasuke have a strong connection in the original series, he might also be involved in the gamer fanfiction, maybe as a rival or teammate in the gaming world.
There could also be new characters introduced in the fanfiction. Maybe a female wizard who befriends Harry in his new form and helps him understand the female side of the wizarding world better. Or perhaps a villain who specifically targets Harry because of his unique transformation, seeing it as a weakness to be exploited.
Obviously, Ash and Erica would be the main characters. Ash is the one who undergoes the transformation, so he's central to the story. Erica is the one who causes the change, so she also plays a crucial role.
She could also change in how she approaches relationships. Before, as a boy, Sasuke was more reserved in his interactions with others, especially with Naruto. But as a girl, she might be more forward in expressing her feelings towards Naruto, whether it's friendship or something more. This could lead to some really interesting character development arcs and new plot directions in the fanfiction.