In a fanfiction where Naruto kills Sasuke at the Uchiha compound, it's a very dark turn. Naruto's character would be severely damaged in the eyes of many. His journey was about saving Sasuke, not killing him. This could also lead to a power vacuum as Sasuke was a powerful shinobi. The Uchiha clan's already tragic story would become even more so. It might also cause Naruto to lose his way, as Sasuke was a sort of mirror to him, and without Sasuke, he might lose his motivation to keep getting stronger.
In a fanfiction where Naruto kills Sasuke and obtains the Sharingan, it would be a game - changer for the story. Naruto would gain new abilities like enhanced visual perception and the potential to use some of the Uchiha's signature jutsu. However, this would also create a lot of internal conflict within Naruto. His ninja way has always been about saving his friends, not killing them. So, this act would make him question his own identity and values. Moreover, the political situation in the ninja world would be in chaos. The Uchiha clan's power being transferred to Naruto, an outsider in terms of the Uchiha, would be a controversial matter that could spark new rivalries and alliances.
If Naruto kills Madara in fanfiction, it could completely shift the power dynamics in the Naruto universe. For one, it might lead to a more peaceful era much sooner as Madara was a major source of conflict. The Akatsuki's plans would likely fall apart without his influence, and the shinobi villages might start to focus more on internal rebuilding and cooperation rather than external threats.
Well, in this fanfiction scenario where Naruto kills the Uchiha clan, it would mean the end of the Sharingan bloodline in a very unexpected way. This would have huge implications for the ninja world. Without the Uchiha, there would be no potential for the Mangekyou Sharingan or the Eternal Mangekyou Sharingan. The balance of power in the ninja world might shift as the Uchiha were quite powerful. And Naruto himself would be a very different character. He's always been about protecting and saving people, so this act would make him a much darker and more complex figure, almost an anti - hero.
Well, in a really dark and twisted fanfiction, Sasuke could be under some sort of mind - control spell. The spell could be so strong that it overrides his feelings for Naruto. He might then attack and kill Naruto without fully realizing what he's doing. But in the real Naruto lore, their friendship and mutual respect are so strong that this is highly unlikely.
One possible reason could be a miscommunication that escalates out of control. Maybe Sasuke is on a path that Naruto believes is too dangerous for the world, and Naruto, in an attempt to stop him, accidentally kills him. For example, Sasuke might be about to use a powerful and uncontrollable jutsu that Naruto fears will destroy the Uchia compound and much more, so he acts in haste.
The Naruto universe would be completely desolate. There would be no more ninja villages, no more clans, and no more shinobi way. It would be a world filled with silence and death.
One possible motivation could be if Sasuke had completely lost his way and was about to do something truly heinous that Naruto had no other option to stop. For example, if Sasuke was about to attack the village or harm innocent people on a large scale.
It would change it drastically. Naruto is known for his loyalty and friendship. If he were to kill his friends, it would shatter the image of the hero. His friends like Sasuke, Sakura, and Shikamaru are important to the overall story and relationships in the Naruto universe. Their deaths at Naruto's hands would create a huge rift among the other characters.
The village's political structure would likely change. Without Danzo, there would be one less power - hungry figure vying for control. The relationship between the Hidden Leaf and other villages might also be affected. Danzo's actions often had far - reaching consequences in international relations. Naruto might face some internal opposition for his actions at first, but in the long run, it could lead to a more just and transparent village governance.
If Sasuke kills Naruto and regrets it, it would completely shatter the hope that Naruto represents in the story. The ninja world, which was slowly moving towards unity because of Naruto, would plunge into chaos. Characters like Sakura would be deeply affected, and Sasuke himself would probably isolate himself even more. His regret might lead him on a new journey of redemption, but the damage to the world would be hard to undo.