In some fanfictions, it might be that Sakura is tricked by a villain who disguises as Naruto. She attacks what she thinks is the enemy in Naruto's form, not realizing it's actually Naruto until it's too late. This would then set off a chain of events in the fanfic world, with characters dealing with the shock and aftermath.
Perhaps there is a situation where Sakura is trying to protect Naruto from a dangerous attack, but due to some unforeseen circumstances, like a misdirected healing jutsu turning into a harmful one, she ends up killing him. It could then lead to a story of guilt, revenge, and the search for a way to bring Naruto back.
In such a fanfiction, one possible storyline could be that Sakura is under some dark magic or mind control which makes her turn against Naruto. Another could be a huge misunderstanding where she believes Naruto has done something unforgivable to her or their friends.
In such a fanfiction, one possible storyline could be that Naruto is somehow mind - controlled and attacks Konohamaru without his own free will. Another could be a situation where there is a huge misunderstanding, like Konohamaru is framed for a serious crime against the village and Naruto, in his overzealous sense of justice, takes extreme action. However, this goes completely against the character development and the bond they have in the original series.
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.
One possible reason could be a sudden and extreme corruption of Naruto's character. Maybe he is influenced by some dark and powerful force that makes him turn against his friends. Another reason might be a misinterpretation of a prophecy or some kind of mind - control situation.
A storyline could involve a time - travel element. Naruto, Sasuke, and Sakura are sent back in time and find themselves in a situation where they have to get married to change the future. They start off as reluctant partners but as they spend more time together in the past, they develop real feelings for each other. They also have to hide their relationship from their past selves and other characters while trying to figure out how to change the future.
Sasuke would likely be filled with rage. He and Naruto had a complex relationship, and Naruto's death at Sakura's hands would make Sasuke seek revenge or at least demand answers. Kakashi, on the other hand, would be deeply saddened. He was Naruto's teacher and would probably feel a sense of failure.
It could be due to a dark influence. Suppose she was under the influence of some dark magic or an evil force that made her lose her true self and turned her against Naruto. This could lead to her almost killing him in the fanfiction.
One possible storyline could be that Naruto is corrupted by a powerful dark force. This force twists his mind, making him see his friends and allies as threats, and he starts killing them one by one. Another could be in a post - apocalyptic Naruto world where resources are scarce, and Naruto has to kill to protect his own group from others who are desperate for food and water.
One possible storyline could be Naruto is depressed because he feels unappreciated in the village despite all his efforts. Sakura, realizing his state, tries to cheer him up by spending more time with him. They start training together and Sakura slowly helps Naruto see his own worth through her belief in him.
One possible storyline could be that Dark Naruto, with his edgier and more troubled persona, saves Sakura from a dangerous situation. This experience makes Sakura see him in a new light and she starts to develop feelings for him. As they spend more time together, Dark Naruto slowly opens up to her about his inner turmoil.