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.
For characters like Itachi, if his spirit or some form of his consciousness was still around in the fanfiction, it would be a complex situation. He sacrificed so much to protect Sasuke, and now Naruto killing him would be a huge irony. Itachi might try to influence the events from the afterlife or through some other means. And Hinata, who loves Naruto, would be deeply concerned for Naruto's state of mind. She would try to support him, but also struggle with the moral implications of what he has done.
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.
There could be. Fanfiction allows for a wide range of interpretations and alternate storylines. But it's a really extreme and disturbing concept considering the bonds that Naruto, Sakura, and Sasuke share in the official story. It would be a very different take on the characters, and most fans who love the original story would probably find it hard to accept.
This type of fanfiction concept is really out of the ordinary. Naruto's character is built on his values of friendship, loyalty, and his dream of becoming Hokage. Killing Sasuke would mean betraying all of that. However, in a fanfiction, the author might be exploring the 'what - if' scenario. For example, what if Sasuke's actions against Konoha were so heinous that Naruto felt he had no choice? But still, it's a far - fetched and very different view from the original Naruto we know.
This kind of fanfiction usually explores alternate storylines and character dynamics. It might be based on intense conflicts or unexpected plot twists.
It's not a very common trope. Most Naruto fanfictions focus on their friendship or the original storylines. Killing off a major character like 'female Sasuke' (assuming it's a gender - bent or AU version) goes against the essence of the Naruto - Sasuke relationship in the main series which is more about rivalry and redemption. So it's not something you'll see often in mainstream fanfiction.
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.
In Naruto fanfiction, the idea of Sasuke killing Naruto is not overly common but does exist in some darker or alternate universe scenarios. Some writers might explore this to show extreme character development or a drastic change in the story's direction. However, it goes against the core of the original series where their relationship is more about rivalry and ultimately friendship.
Yes, there are likely some fanfics out there with such a plot. Fanfiction is a creative space where authors explore different scenarios. However, it goes against the general narrative of the Naruto series where Naruto is more about saving Sasuke.