For Ron and Hermione, they would likely be devastated at first, thinking they had lost their best friend. But then they might start to suspect something when they notice small details that don't add up. Ginny would be heartbroken and might become more determined to fight against Voldemort in revenge. The Order of the Phoenix would be in chaos, with some members losing hope while others might start to investigate the circumstances of his 'death' more closely.
Maybe he used some rare magical artifacts. In the wizarding world, there are many mysterious items. He could have found an artifact that allows him to project an image of his death while he actually hides in a magically protected place. It's also possible that he faked his death by making a deal with some magical creatures that are good at deception, like the house - elves. They could have used their magic to make everyone believe he was dead.
The Death Eaters might think they've won at first. There could be chaos and fear among the good wizards. But it could also lead to a secret resistance growing stronger.
Harry is the main one as it's his faked death. Hermione, with her sharp mind, would be a mainstay in the story. Ron, with his loyalty and bravery, would be right there. Neville could also be a main character. He has grown a lot throughout the series and could be involved in the events surrounding Harry's faked death, perhaps even being one of the first to suspect something fishy. And then there's Ginny. As Harry's love interest, she would be deeply affected by his faked death and would be a central figure in the emotional turmoil of the story.
One possible scenario could be that Harry uses Polyjuice Potion to create a false body that appears to be his dead self. He might do this to deceive Voldemort and his Death Eaters, giving him the element of surprise to strike back later. Another scenario could involve elaborate magical illusions created with the help of his friends, like Hermione's extensive knowledge of spells and Ron's courage in the face of danger. They could set up a staged death scene that looks very real to the outside world.
One possibility is that Harry uses some advanced and little - known magic. He could have found a spell in an ancient book in the Room of Requirement. This spell might allow him to project an image of his death while he actually hides himself in a magically protected space. He may also have made arrangements with the Order of the Phoenix to spread the news of his death convincingly.
In such a fanfic, a really interesting plot twist could be that Harry fakes his death and as a result, Hogwarts itself undergoes some major changes. The school becomes more secretive and starts to develop new security measures thinking Harry is gone and they need to protect themselves better. Or perhaps Harry fakes his death and it turns out that there was a prophecy that predicted this event all along. This prophecy then leads to new revelations about his true purpose and the future of the wizarding world.
One possible plotline could be that Naruto fakes his death to protect the village from a powerful enemy who has a vendetta against him specifically. He might do this to draw the enemy out and expose their weaknesses.
It could be a new, powerful ninja who has a vendetta against Naruto. This antagonist might be jealous of Naruto's popularity and power, and wants to take over the Hidden Leaf Village.
One possible plot could be that Naruto fakes his death to outwit a powerful enemy who has been targeting him directly. By doing so, he can secretly gather information and plan a counter - attack.