In the fanfiction, Naruto might fake his own death by staging a big battle. He could have used shadow clones to create a scenario where it appears he's been killed. He might have also had help from some allies who are good at creating illusions or covering up his tracks. For instance, they could have made it look like his body was completely destroyed in the fight, when in reality he was just hiding somewhere safe waiting for the right moment to reveal himself.
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.
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.
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.
His friends might feel betrayed. They would be mourning his death while he was actually alive. This could lead to a lot of anger and mistrust when they find out the truth.
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.
A secret organization that has been operating in the shadows and views Naruto as a major threat to their plans. They might be planning something big like taking over the ninja world, and Naruto's presence and influence stand in their way. So, Naruto fakes his death to gather intelligence on this organization without alerting them.
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.
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.
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 consequence could be that his friends are devastated at first. They might go through a period of grief and self - blame for not being able to protect him.
Another possibility is that the main antagonist is a group. It could be a secret organization that Naruto discovers is plotting something big. Since they are so powerful and well - connected, Naruto fakes his death to infiltrate them and expose their plans from the inside.