It could be a new character entirely. Maybe a rogue ninja from a long - forgotten clan who holds a grudge against Naruto for some past event. This villain could be extremely powerful in dark jutsu and sees Naruto's death as the first step in his plan to take over the ninja world.
Perhaps an old enemy from Naruto's past that was thought to be defeated but actually managed to survive and regain strength. This villain might have a vendetta against Naruto for imprisoning him or causing the downfall of his organization. After Naruto's death, this villain could target Boruto, seeing him as a symbol of Naruto's legacy and wanting to break the will of the Hidden Leaf Village.
There is also a possibility that the main villain is a corrupted version of one of Naruto's friends or allies. This could be due to some dark influence or a tragic event that twists their mind. They could be the one responsible for Naruto's death, either directly or indirectly, and then become the main threat that Boruto has to face in the fanfiction.
One possible plot could be that Naruto sacrifices himself to save Boruto from a powerful new enemy. Maybe an ancient evil resurfaces that is too strong for Boruto to handle alone, and Naruto steps in, using up all his chakra and ultimately dying in the process.
It could be an unknown, ancient evil that has been awakened. This villain might have powers far beyond what Naruto and Sasuke have faced before. Maybe it's an entity from a forgotten era that was sealed away long ago and now has broken free.
Boruto's reaction would be complex. He'd be heartbroken, for sure. He might start to question his own worth and purpose. But over time, he'd realize that he has to carry on Naruto's legacy. He'd become more serious and focused. He'd also become more empathetic towards others, understanding the weight of sacrifice. He might even start to study Naruto's techniques and leadership style more closely, trying to emulate the things that made Naruto such a great Hokage and hero.
One possible plot could be that Naruto sacrifices himself to protect Boruto from a powerful new enemy. Maybe an ancient evil has been awakened and Boruto is in its direct path. Naruto, being the hero he is, steps in and uses all his power to stop it. His death then becomes a catalyst for Boruto's growth, driving him to become stronger and more determined to protect the village in Naruto's memory.
There could be a scenario where Naruto sacrifices himself to save Boruto or the entire Hidden Leaf Village from a catastrophic event like a massive attack by an unknown and dangerous force. He might use all his chakra to protect the village, leaving him with no energy to survive.
In a 'naruto dies boruto fanfic', Boruto's character would go through a major transformation. He would be forced to grow up overnight. Initially, he might be consumed by anger and a desire for revenge if Naruto was killed unjustly. But as time passes, he would learn to channel that energy into positive change. He would study his father's leadership style and try to implement it in his own way. He would become more diplomatic, forging alliances with other villages to strengthen Konoha's position. His sense of justice would be refined, and he would be more committed to protecting the world his father loved so much.
At first, Boruto would be in shock. But then, he would likely be filled with a new - found determination. He would vow to become as strong as Naruto, if not stronger. He'd study Naruto's techniques more intently and strive to protect the village in Naruto's place. Boruto would also carry the weight of Naruto's legacy on his shoulders, which would shape his actions and decisions in the fanfiction.
In the 'naruto dies boruto fanfic', it could be that Naruto is killed by an unexpected betrayal within the village. This shatters Boruto's world. He then goes on a journey to find out the truth behind the betrayal. Along the way, he meets some of Naruto's old friends who help him train and grow stronger. Boruto also starts to uncover secrets about the village's past that his father was trying to protect, and he realizes he has to be the one to expose these secrets and bring justice to his father's death.
Perhaps there's a prophecy involved. The fanfic could be set up where it's foretold that Boruto will bring about a great change, but only if he survives a certain threat. Naruto, aware of this, sacrifices himself to ensure Boruto lives on. This could then trigger a series of events where Boruto has to deal with the political fallout in the village, as some may blame him for Naruto's death, while others see him as the key to the future. It could also lead to a rift between Boruto and some of his friends who struggle to understand why Naruto had to die for him.
If Naruto dies in the fanfic, Boruto would likely face a great emotional turmoil. He would have to grow up without his father's guidance, which could make his journey to become a ninja even more challenging. Also, the Hidden Leaf Village would lose its strongest protector, which might lead to a sense of insecurity among the villagers.