Jiraiya, if he were still alive in the fanfiction, would be a crucial character to help Naruto. He was Naruto's mentor and had a vast amount of knowledge. He could use his sage techniques to both protect Naruto and find a way to heal his wounds. Tsunade, as the Hokage, would also mobilize all available resources in the village to ensure Naruto's safety and recovery. Shikamaru, being one of the more intelligent characters, would come up with plans to deal with the situation while Naruto is wounded.
Temari, Gaara's sister, is also very likely to rush to his side. She is protective of her younger brother and has great combat skills. She would be there to both defend him from further harm and to help him heal, using her knowledge of medical ninjutsu if she has any.
Liz and Patty would be the most obvious ones. They are his weapons and also his friends. They are always by his side and would do anything to protect him. So when he gets hurt, they would be right there to try and help him, whether it's by fighting off any remaining threats or trying to find medical help.
Gajeel is very likely to come to her aid. He has a special bond with Levy, so when she gets hurt, he would be one of the first to rush to her side. He might use his iron dragon slayer magic to protect her from further harm or carry her to safety.
Sakura is very likely to help. She's a skilled medical ninja and has always been there for Naruto. She would use her medical jutsu to try and heal his wounds. Kakashi too. He has a lot of experience and would be able to protect Naruto while he's injured. Also, Sasuke might come to Naruto's aid. Despite their past differences, they have a deep bond, and Sasuke would not let Naruto die if he could help it.
Sasuke could be a likely character in some fanfiction. Maybe in an alternate universe where their rivalry takes a darker turn, Sasuke might frame Naruto to gain an advantage or to prove his own superiority. It would add a whole new dimension to their relationship.
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.
Definitely Naruto is the central figure. In the harem, Hinata is a very likely character since she has always been in love with Naruto. Sakura might also be there as she has been one of Naruto's closest friends. Tenten could be another addition. She has interacted with Naruto in the series and could potentially be part of the harem in this fanfiction. Also, Temari, who has had some interesting encounters with Naruto, might be a character in the harem as well.
One of the likely supporting characters is Tsunade. Given her experience and leadership in the village, she could be a source of advice for Naruto and Hinata. She might also ensure that Hinata has the best medical resources available during her pregnancy. Rock Lee could be another supporting character. His positive attitude and loyalty to Naruto would make him eager to help out. He could be running errands for them or helping with any physical tasks. And Neji, if he were still alive in this fanfiction, would surely be there to protect his cousin Hinata and support Naruto as well.
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.