Well, it would be a really dark plot. Maybe Sasuke, consumed by his thirst for power or revenge, finally overcomes Naruto in a brutal battle. This could lead to a world in chaos as Naruto was the hope for many. The Hidden Leaf Village would likely be in a state of despair, with all the friends of Naruto vowing revenge on Sasuke.
One possible scenario could be a power imbalance. Maybe Sasuke discovers some new, extremely powerful jutsu that Naruto has no defense against. For example, a jutsu that can nullify Naruto's chakra or attack his spirit directly. Another possibility is a miscommunication or a breakdown in their relationship. If Sasuke believes Naruto has betrayed him in some way, his anger could lead him to kill Naruto. However, this goes against the core of their bond in the original series.
Sakura would be devastated. She has deep feelings for both Naruto and Sasuke. She might turn against Sasuke completely and try to take revenge herself. Kakashi would be in shock. He has mentored both and would likely feel like he failed in some way. As for the other ninja from the Hidden Leaf, they would be angry and mournful at the loss of their hero Naruto.
It's not that common, really. The main narrative of Naruto is centered around their friendship and rivalry, not one killing the other in a definitive way. Most fanfiction focuses on their growth and development together rather than such a tragic end for Naruto at Sasuke's hands. However, there are a few out there that might explore this for shock value or to create an alternate universe scenario.
The story could develop in a very dark direction. Sasuke might be filled with regret immediately after killing Naruto. This could lead to him isolating himself from the rest of the ninja world as he grapples with his actions. The ninja villages might be in chaos as Naruto was seen as a symbol of hope. Without him, there could be power struggles among different groups.
Sakura is often quite popular. In college fanfiction, she might be a brilliant medical student, still having her feelings for Sasuke while also becoming good friends with Naruto. Her strong - willed nature and intelligence can add a lot to the story.
It could be a random civilian. This would show Naruto the impact of the ninja world's violence on ordinary people, making him more determined to protect the innocent.
Kakashi Hatake is a popular choice. He has a long history with both Naruto and Sasuke, having trained them. He could be included to offer guidance or add some comedic moments. For example, he could give them some tough training exercises that help them bond more. Another popular character is Sakura Haruno. She has her own complex relationship with both Naruto and Sasuke. Her presence can add some drama, like if she has to choose between helping Naruto or Sasuke in a difficult situation.
I think Kakashi could be really popular. Since he has a connection to both Sasuke and Naruto, his role in a time - travel story could be very interesting. He might be able to help them adjust to the past or use their knowledge to his advantage. Another popular character could be Itachi. His actions in the past are so crucial to the story, and in a time - travel scenario, he could interact with Sasuke in a whole new way.