Well, it could be that Naruto sacrifices himself to seal away a dark and ancient curse that is threatening to destroy not only the ninja world but all of existence. He realizes that his unique connection to the tailed beasts and his strong willpower make him the only one who can perform this self - sacrificing sealing jutsu. So, he says his goodbyes to his friends, family, and the village he loves and gives up his life to save everyone.
One possible plot could be that Naruto has to sacrifice himself to break a powerful genjutsu that has enslaved the entire ninja world. This genjutsu is so strong that it can't be broken in the normal way. Naruto discovers that by giving up his own life force, he can shatter the illusion. He makes this choice knowing the cost, but also believing that it will bring peace and freedom back to the world. He entrusts the future of the village and his friends to his proteges like Boruto and the new generation of ninjas.
One possible plot could be that in a final battle against an extremely powerful enemy, Naruto realizes that the only way to save Hinata and the entire village is by using a forbidden jutsu that will cost him his life. He makes this sacrifice with a smile on his face, knowing that Hinata and the others will be safe. Hinata is heartbroken but also determined to carry on Naruto's legacy of protecting the village.
In the fanfic, it could be that Fleur is in a situation where she has to perform a dangerous task to save the wizarding world, like going into an ancient and deadly magical place. Harry, realizing the importance of her mission and also having deep feelings for her (maybe a secret love), sacrifices his own safety by going with her and ultimately giving his life to ensure she can complete the task and save everyone.
One possible plot development could be that Sasuke is initially in a situation where he is facing an enemy he can't defeat alone. Naruto steps in and gives his life to save Sasuke. This would lead to Sasuke being filled with guilt and a new sense of purpose. He might vow to carry on Naruto's will, perhaps trying to bring peace to the ninja world in Naruto's name. Sasuke could also start to question his own actions that led to Naruto having to sacrifice himself, and he may become more empathetic towards others as a result.
In the fanfiction, Naruto might sacrifice himself for Sakura in a more selfless act of love. For example, if Sakura is afflicted by a deadly curse and the only way to break it is for someone to transfer all their life energy to her. Naruto, being the selfless hero he is, decides to do it without hesitation. This would then explore how the other characters react to his loss and how Sakura copes with living on with Naruto's gift.
It could be a long - lost Uchiha with powers beyond that of Madara. This Uchiha could have been in hiding, gathering power and knowledge, and his ultimate goal is to reshape the world in his own dark image. Naruto realizes that the only way to stop him is by sacrificing himself.
One possibility is that Percy sacrifices himself to save his friends and Camp Half - Blood from a powerful, unbeatable enemy like an ancient primordial god. He might use his powers to create a shield or diversion that allows everyone else to escape while he faces certain death.
In such a fanfiction, the plot could involve Naruto sacrificing himself to save the Hidden Leaf Village from a powerful and seemingly unstoppable enemy. Maybe it's a new, more menacing form of the Akatsuki that has emerged with a doomsday - like jutsu. Naruto, being the hero he is, decides that the only way to protect his friends and the village is by using a self - destructive jutsu that nullifies the enemy's power but at the cost of his own life. His sacrifice could lead to a period of mourning in the village, with his friends like Sasuke feeling guilty for not being there to prevent it and vowing to carry on Naruto's legacy of peace.
Perhaps in the fanfiction, Naruto gives his life energy to Boruto to save him from a deadly curse. Boruto then has to deal with the newfound power within him, which is a mix of his own and his father's. He may struggle to control it at first but eventually learns to use it for good. This could also lead to a rift between Boruto and some of the villagers who blame him for Naruto's death.
Well, the Kyuubi itself would probably be changed. Naruto had a deep bond with it. His sacrifice might make the Kyuubi more empathetic towards humans. It could even decide to protect the village in Naruto's memory. On the other hand, the next generation of ninja would grow up without Naruto as their inspiration. They would have to find new heroes to look up to, and the stories of Naruto's deeds would become more like legends, with a bittersweet feeling of what could have been if he had lived.
In such a fanfiction, one possible plot could be that Naruto faces an extremely powerful enemy who is about to kill Kakashi. Naruto, being the selfless hero he is, steps in and uses a powerful jutsu that requires sacrificing his own life to save Kakashi. This could lead to a great deal of mourning among the other characters, especially those close to Naruto like Sasuke and Sakura. They might then vow to carry on Naruto's will and protect the village even more fiercely in his memory.