Kakashi Sensei could also be involved. He is Naruto's teacher and mentor. If Naruto gets hurt during a mission that Kakashi is leading, Kakashi would surely be there. He might feel responsible for Naruto's injury and would do everything he can to protect him further and get him to safety. And then there's Pain. In some fanfics, Pain could be the one who attacks Naruto and causes him to get hurt, especially if the fanfic is centered around the events related to Pain's invasion.
Definitely his friends from Camp Half - Blood. Percy Jackson, for instance, would be likely to be involved. He might be the one to find Nico when he's hurt or be part of the group that's trying to rescue him. Annabeth could also be involved as she is often in the thick of things and would use her strategic mind to help Nico when he's injured. Hazel, being his sister, is very likely to be there. She would be extremely worried and do whatever she can to heal or protect him.
Well, Sasuke could be involved. He might be the one who finds Sakura when she's hurt and has to deal with his feelings for her while trying to get her help. Naruto is also a likely character. He could be devastated by Sakura's injury and vow to get revenge on whoever caused it.
Erak might be an unexpected character to help. Despite his rough exterior, he has a sense of honor. If he happened to be in the area when Will gets hurt, he could offer his ship as a means of quick transport to a place where Will can be treated. Also, the apprentices that Will has trained. They would look up to him and would be eager to repay his kindness. They could run errands, gather herbs for medicine, or keep watch while Will recovers.
Obviously Naruto himself is the central character as the story is about him getting disowned. His friends like Sasuke and Sakura might also be involved. Sasuke could be conflicted between his loyalty to the village and his friendship with Naruto. Sakura might initially be confused about whether to side with the village or Naruto. And then there are the village elders like Danzo who could be the ones behind Naruto's disownment in the fanfic.
Obviously, McGee is the central character as he's the one getting hurt. Gibbs would surely be involved. He'd be the one leading the investigation into McGee's injury, using his no - nonsense approach. DiNozzo would also be there, probably cracking some inappropriate jokes at first to lighten the mood but then getting serious as the situation unfolds.
Even some of the enemies of the Kanes could be involved in a different way. For instance, if Carter was hurt by a particular enemy, that enemy would be a central figure in the fanfiction. But there could also be unexpected allies among the enemies. Maybe a lower - ranked enemy realizes that Carter's death or continued injury could lead to a worse situation for them all, and they end up helping in some way, either by providing information about the cause of the injury or by secretly protecting Carter from their more evil comrades.
Sasuke is very likely to be involved. Given their complex relationship, Sasuke could be the one who finds Naruto severely injured and has to make a choice between helping him or leaving him. Another character could be Sakura. As a medic - ninja, she would be the one to try and heal Naruto's severe injuries. Kakashi too might be involved, either as a mentor figure who tries to figure out what happened to Naruto or as someone who has to step in to protect Naruto from further harm while he is injured.
Obviously Naruto himself is the main character involved. But his friends like Sasuke, Sakura, and Kakashi are also likely to be involved. Sasuke might be affected by Naruto's wishes, for example, if Naruto wishes for Sasuke to fully return to the Hidden Leaf Village and be at peace. Sakura could also be involved, perhaps in helping Naruto make his wishes come true in a medical or support way. And Kakashi, as Naruto's former teacher, would surely play a role in guiding Naruto in how to use his wishes wisely.
Kakashi could also be an important character. He has a lot of experience and wisdom. When Naruto gets high, Kakashi might be the one to guide Naruto through this strange state, using his own past experiences and knowledge of different ninja techniques. And then there's Jiraiya. Given his relationship with Naruto, he would surely be involved, perhaps trying to use his own unique jutsu to help Naruto come back to normal.
Hinata would also play a major role. Since she has deep feelings for Naruto, she would be devastated by his amnesia. She might try to use their shared memories, like the time she confessed her love to him during the Pain attack, to jog his memory. And the Akatsuki members could also be involved in some cases. If Naruto's amnesia was caused by their actions, they might be the antagonists in the fanfiction, or they could also be trying to use his amnesia for their own purposes.