Perhaps the village is invaded by a horde of powerful demons. Naruto, after a long and grueling battle, realizes that the only way to stop them is to seal them all away, like the way the Fourth Hokage sealed the Nine - Tails. But this sealing jutsu demands the life of the caster. Without hesitation, Naruto performs the jutsu, sacrificing himself to save the village he loves so much.
It could be a rogue ninja who has mastered a forbidden jutsu and wants to destroy the village out of revenge. Naruto would then have to face this extremely powerful foe and in the end, sacrifice himself to stop the destruction.
In this fanfiction scenario, Naruto might die while saving Tsunade from a sneak attack. His death could cause a shift in the power dynamics of the village. Tsunade, filled with guilt and grief, could then take on a more reclusive role. Meanwhile, the younger generation, seeing Naruto's selfless act, would strive to uphold his ideals. They might start training harder and be more committed to protecting the village, just as Naruto did.
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.
In such a fanfiction, one possible plot development could be that Naruto sacrifices himself during a major battle against an extremely powerful enemy. Maybe an enemy that has the power to destroy the entire Hidden Leaf Village. Naruto, being the hero he is, steps in to protect Hinata and in the process, takes a fatal blow meant for her. This would lead to great sorrow among the villagers, especially Hinata who would be heartbroken. She might then vow to carry on Naruto's will and protect the village in his memory.
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.
One possible plot could be that Naruto and Kakashi are in a fierce battle against a powerful enemy. Kakashi is about to be fatally attacked when Naruto jumps in front of him and takes the hit. As Naruto is dying, he might have some final words for Kakashi, perhaps about the importance of protecting the village and their friendship.
One possible plot could be that Fem Haku has some sort of unique ability or knowledge that is crucial for the safety of the Hidden Leaf Village. Naruto and Fem Haku are being pursued by an evil organization that wants to stop her from reaching the village. Along the way, they face numerous obstacles and battles. In a final showdown, Naruto realizes that the only way to ensure Fem Haku's survival and the safety of the village is to sacrifice himself. He gives his life to protect her, and Fem Haku then has to deal with the consequences of his death, like facing the villagers who may blame her, and also has to figure out how to use her abilities to protect the village on her own.
One possible plot could be that Sarada gets into a dangerous situation, like being attacked by a powerful enemy. Sakura, being her mother, jumps in to protect her without hesitation. Sakura uses all her medical ninjutsu skills and combat abilities to fend off the enemy, but in the end, she sacrifices herself to ensure Sarada's safety.
It could also be part of a more complex plot where Naruto has made a promise to protect Ino at all costs. There might be a prophecy or some sort of dark force threatening the village and Ino is specifically targeted. Naruto, knowing the importance of her life for the village or for some other deeper reason, gives up his own life to ensure her safety. This could lead to a great deal of character development for the other characters as they deal with Naruto's sacrifice.
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.