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.
Perhaps he has discovered a great threat that is specifically targeting him. To keep the village and his family from being collateral damage, he fakes his death. This way, he can secretly gather information, train more, and come back stronger to face the threat when the time is right.
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.
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.
It could be Orochimaru. Even though he's had his moments of redemption, he might relapse into his old ways. He could see Naruto's 'death' as an opportunity to carry out some evil plan that Naruto would have stopped. Maybe he wants to use Naruto's death to create chaos and then take advantage of the power vacuum in the ninja 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.
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.
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.
The reason Teng Zijing faked his death was to protect Fan Xian. In the plot, after Teng Zijing received Fan Xian's help, he could have left the place of trouble and reunited with his wife and children. However, in order to protect Fan Xian, he chose to stay and pretended to be killed by the Northern Qi expert Cheng Jushu. Teng Zijing had made this choice because Fan Xian had always been helping him. If it were now, he would be able to help an old man up without thinking when he saw him fall. On the other hand, after Teng Zijing had helped the bullied couple, he had been bitten back in court. This made him feel helpless. Helping someone up was only to be blackmailed. Teng Zijing's fake death provided a turning point in the plot's development and also made Fan Xian feel touched by his sacrifice.
The reason Teng Zijing faked his death was to protect Fan Xian. In the plot, after Teng Zijing received Fan Xian's help, he could have left the place of trouble and reunited with his wife and children. However, in order to protect Fan Xian, he chose to stay and pretended to be killed by the Northern Qi expert Cheng Jushu. Teng Zijing had made this choice because Fan Xian had always helped him. He was grateful and loyal to Fan Xian. On the other hand, Teng Zijing was also a very kind person. After he helped the bullied couple, he was bitten back in court. This made him feel that there were similarities to the " helping someone but being blackmailed " in the past. Thus, in order to protect Fan Xian and uphold justice, Teng Zijing chose to fake his death.