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.
He could have used his connection with the Deathly Hallows. The Invisibility Cloak could have been used in a more advanced way, combined with some other spells to make it seem like he was no longer alive. The Resurrection Stone might also play a role. He could have created an apparition of himself that appears to die, while his real self remains hidden. His knowledge of the Elder Wand could also give him the power to deceive death in some way, as it is the most powerful wand and might have abilities not fully known.
Well, Naruto could have made a deal with some powerful being or used some sort of forbidden technique. Maybe he found a way to transfer his life signs to another object or being, making it seem like he was dead. He's always been resourceful and full of surprises, so faking his own death in a really elaborate and unexpected way is not out of the question.
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.
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.
Well, he might use some substitution jutsu. He could replace himself with a log or something similar at the crucial moment, making it seem like he's been killed.
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.
His best friends Hermione and Ron would be the most likely candidates. Hermione's intelligence and vast knowledge of magic could come up with a complex plan to fake Harry's death. Ron, with his loyalty and bravery, would be there to support and execute the plan. They have been through so much together that they would be willing to take such risks for Harry.
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.
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 reason could be to protect his family. After the war, Naruto might have made many enemies. By faking his death, he could draw the attention of these enemies away from his family, especially his wife and children. His enemies would think he's no longer a threat and stop targeting his loved ones.
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.