His best friends, Ron and Hermione, would probably be the most affected. They're used to seeing him with his old hair, so the change might be a shock at first.
Obviously, Harry Potter himself is the most directly affected as he doesn't survive. But then there are his friends like Hermione and Ron. They would be deeply affected, probably filled with grief and guilt. Hermione might blame herself for not being able to come up with a better plan to save Harry. Ron would be devastated, as Harry was not only his best friend but also like a brother to him.
Well, perhaps Harry's new haircut makes him look completely different and his friends don't recognize him at first. It could be a humorous situation where they keep asking who he is until he reveals himself.
Well, it could change the Hogwarts curriculum in fanfic. Maybe they'd start teaching spells for radiation protection or how to deal with post - nuclear landscapes. And the houses could be re - sorted based on how students react to the threat of nuclear war. Gryffindors might be more likely to volunteer for dangerous missions to help the outside world, while Ravenclaws could be researching magic - based solutions to the nuclear fallout.
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.
His friends would surely be affected. Ron and Hermione might be in awe of his newfound powers. They could also benefit from his abilities. For instance, Harry could use his time - traveling ability to save Hermione from the time - turner accident. And Ron could get some special training from Harry to become a much more powerful wizard himself.
His friends would surely be affected. Hermione and Ron might be both amazed and a bit worried. They could be worried that this new power might change Harry too much or put him in more danger. Also, his enemies like Draco Malfoy would be affected. Draco might become more jealous or even more afraid of Harry.
The Death Eaters themselves would be affected in an interesting way. Some might welcome Harry with open arms, but others might be suspicious of his sudden change of sides. They might fear that it's a trick by the Order. And within Hogwarts, the students would be in turmoil. Those who idolized Harry would be heartbroken and confused, and there could be a split among the student body depending on who believes Harry's new stance.
Definitely Hermione. Since she's Harry's closest friend and very intelligent, she would be deeply involved in any changes Harry tries to make. Also, Snape. Harry's actions in the past could completely change his relationship with Snape. And of course, Voldemort. If Harry goes back far enough, he could potentially stop Voldemort's transformation into the evil wizard he became.
Ruby. She's always evolving and going through big changes. A dramatic haircut for her could signify a major shift in her character arc. Maybe after a loss or a great discovery, she decides to cut her hair short as a way to show she's no longer the same innocent girl who started out at Beacon Academy.
The fandom would be divided. Some fans who are deeply into fanfiction would be disappointed and might feel like a part of their connection to the 'Harry Potter' world has been cut off. However, others who are more focused on the official works might not be as affected. There would likely be a decrease in the variety of fan - created stories, which could limit the creative exploration within the fandom.