The plot could involve Kakuzu being controlled by a more powerful and evil force. Naruto, after trying to reason with him and failing, has no choice but to kill him. This could also be a part of Naruto's growth, where he realizes that sometimes, in the face of extreme evil, killing is the only option to protect others.
Kakashi could be a significant supporting character. He could provide Naruto with some advice or even join the battle alongside Naruto for a while. Another possible supporting character could be Hinata. Her gentle presence and belief in Naruto could give Naruto the extra motivation he needs during the fight.
In an 'Obito kills Kakashi' fanfiction, it could start with a long - standing grudge. Maybe Obito discovers some new information that he believes Kakashi has been hiding from him all these years. This enrages him so much that he decides to take revenge and kills Kakashi in a fit of rage during a battle.
One reason could be a misunderstanding. Maybe some false information makes Naruto think Kakashi is a traitor to Konoha. So, in a fit of rage, he kills Kakashi. Another reason could be related to power. If Naruto becomes obsessed with power and Kakashi tries to stop him from going down a dark path, Naruto might lash out and kill him.
Some fans would be really shocked and sad. Kakashi is a very popular character, and his death at the hands of Obito would be a huge blow to many. They might feel angry towards the author for creating such a tragic scenario.
Well, if there is a 'naruto kills kakashi fanfiction', it would be a very different take on the Naruto universe. It could be set in a world where Naruto has been corrupted by an evil force. This force could be manipulating Naruto's emotions and memories, making him think Kakashi is a threat. In the original series, they have a strong bond, so this would be a very controversial and unexpected plot.
One possible motive could be mind control. Maybe an enemy manages to take over Kakashi's mind and forces him to harm Naruto. Another could be a misunderstanding. For example, if Naruto was thought to be possessed by a powerful and dangerous entity that Kakashi believed could only be stopped by killing Naruto.
The story would likely take a very dark turn. Team 7 would probably be hunted by the village. They would become outcasts and have to constantly be on the run. Their relationships with other characters would be completely shattered.
Sasuke would be extremely angry. He and Naruto had a complex relationship that evolved from rivalry to friendship. His first reaction would likely be to seek vengeance. Kakashi himself would be filled with guilt and self - loathing. He has always been Naruto's teacher and protector in a sense. Hinata would be heartbroken. She had deep feelings for Naruto. The rest of the village would be in shock and disbelief. Naruto was seen as their future, and his sudden death at Kakashi's hands would create a sense of despair and confusion.
Another motive might be related to some dark power corrupting Team 7. This power could have twisted their minds and made them see Kakashi as an obstacle in their path to achieving ultimate power. It could be something like the curse mark in the original Naruto series but even more powerful and insidious.