His close friends like Sasuke and Sakura would likely be among the most affected. They know Naruto well and seeing him in a terrifying state would be very shocking for them. For Sasuke, who has a deep bond with Naruto, it would be especially hard to face a scary Naruto.
His enemies, too, would be affected but in a different way. They are used to Naruto being a certain kind of threat, but a truly terrifying Naruto would make them question their own abilities to face him. They might start to panic and make hasty decisions because they fear the new, scarier Naruto.
Hinata would also be highly affected. She has always admired Naruto from afar. By seeing his memories, she would understand him on a whole new level, his struggles, his hopes, and it would likely strengthen her feelings for him even more. And it could also change how she interacts with him in the story.
Sasuke would definitely be one of the characters often affected. Since he has such a complex relationship with Naruto, any unexpected action from Naruto would surely impact him. For instance, if Naruto suddenly decides to change his approach towards bringing Sasuke back to the village in a very radical way.
In the fanfiction, Naruto could have been possessed by some dark force. This dark - Naruto then starts to act in a very unpredictable and scary way, like randomly attacking people with great force. He might also have a really creepy look in his eyes, which scares everyone around him. The villagers who once knew Naruto as a friendly ninja would be shocked and terrified.
His friends from U.A. High School such as Bakugo, Ochaco, and Iida would also likely be main characters. Since Izuku is scaring everyone, they would be the ones experiencing the fear and trying to figure out what has happened to him. Their reactions and attempts to deal with the situation would be important parts of the story.
His classmates like Bakugo could be a main character. Bakugo might be one of the first to notice the strange changes in Izuku and could be both scared and angry about it. He might try to confront Izuku, which could lead to some intense scenes.
His closest friends like Ron and Hermione would probably be the most affected. They are used to having Harry around and relying on him. His sudden ignoring would leave them confused and worried.
Sasuke would be one of the most affected. He and Naruto had a complex relationship, from being rivals to friends. Naruto's death would leave a huge void in Sasuke's life. Also, Hinata. She loves Naruto deeply, and losing him would be devastating for her.
The other students at Hogwarts would also be affected. For example, Neville, who looks up to Harry. If Harry ignores everyone, Neville might feel lost. Ginny, who has a special connection with Harry, would be deeply hurt. And the teachers like Snape, who has a complex relationship with Harry, would also be impacted. Snape might be secretly glad at first, but then realize that Harry's isolation could be a sign of a bigger problem in the wizarding world.
Family members, if he has any in the fanfiction world, would be devastated. His mother, for instance, would have to deal with the loss of her son. She might become more involved in the affairs of the demigod world, trying to make sure that her son's sacrifice was not in vain. Also, his half - siblings, if any, would be affected. They could be inspired to step up and prove themselves worthy of Percy's sacrifice.
Ruby could be one of the most affected. Her leadership role might be put to the test as she tries to keep her team and others safe from the virus. Also, her innocent and positive nature might be challenged by the dark reality of the virus situation.