It could be a rogue ninja from another village who has a vendetta against Naruto. This ninja might have set a very elaborate trap that made it seem like Naruto was killed and left his body in a place where his friends would find him and think he was dead.
Maybe Naruto is betrayed by someone within the village who sets him up to look like he's dead. Left for dead, he's found by a hermit who teaches him new and powerful jutsu. With his new skills, he plans to return to the village to expose the traitor and prove his worth once again.
He might survive through his own sheer willpower. Naruto has always been a tenacious character. So, even when left for dead, his determination to live and achieve his dreams could keep him alive against all odds.
Iruka Sensei could also be a candidate. He was one of Naruto's first supporters and has a deep connection with him. He would probably risk a lot to save Naruto.
Perhaps there was some sort of dark influence or mind - control at play. An enemy might have manipulated Kakashi's mind in such a way that he believed Naruto was a threat and thus left him for dead, not realizing his true self.
One possible reason could be a misunderstanding. Maybe they were misled by false information or an enemy's trickery that made them think Naruto was a threat at that moment. Another reason might be extreme pressure or a life - or - death situation where they thought sacrificing Naruto was the only way to save the rest of the team or complete a crucial mission.
One possible plotline could be Naruto finding unexpected allies during his time left for dead. Maybe some characters who previously had no connection to him come to his aid out of a newfound sense of justice or a change of heart.
Another plotline might involve Naruto's inner struggle and growth. He could discover new powers or a deeper understanding of his ninja way while on the verge of death. He might have to rely solely on his wits and the training he's had in the past to survive. For example, he could use his shadow clones in more creative and strategic ways to defend himself and find a way back to his village.
Kakashi could also play a role. He has always been a mentor to Naruto and his sense of duty and loyalty to his student might drive him to search for Naruto when he hears that he's been left for dead. He has the skills and knowledge to find and save Naruto in a difficult situation.
Initially, Naruto could be filled with anger. He might feel like all his efforts to protect the village and be accepted were in vain. However, his strong will and belief in himself would likely kick in. He could decide to train even harder, not just to prove his innocence but also to become strong enough to face whatever force was behind his betrayal. He might also start to question the values of the village he once held so dear.