If Naruto kills the Sandaime in a fanfic, it would likely set off a chain reaction of events. Firstly, Naruto's friends like Sakura and Sasuke would be in a difficult position. They might not believe it at first or would try to find out the real reason behind it. The village's structure would start to crumble as there would be a power vacuum. And Naruto himself would be on a path of self - destruction or redemption, depending on how the fanfic is written.
It would be chaos. The Sandaime was a symbol of stability in Konoha. His death at Naruto's hands would make Naruto an instant outcast. The villagers who once hated him might now fear and hunt him. It would also shatter the trust between the different ninja clans and those who supported the Sandaime's leadership.
In a 'Naruto kills the Sandaime' fanfic, it would be a very dark and alternate take on the Naruto universe. This goes against the traditional bond and respect Naruto has for his village elders. It could be a result of some extreme corruption within the village that Naruto discovers, leading him to take such a drastic step. However, this is a huge deviation from the original storyline.
Well, Naruto might become extremely powerful. The Sandaime Hokage has a wealth of knowledge and skills. He could teach Naruto some very unique jutsu and also help him better understand the values of the village. Maybe Naruto would grow faster in terms of combat skills and leadership abilities.
The story would take a different turn. Naruto would have more support. The Sandaime could help him train better and understand his powers more. Also, the threat from Orochimaru might be more easily managed, which would change the whole dynamic of the series.
Well, one possibility is that Naruto would face some serious consequences. Killing is not in his usual nature, so he might struggle with guilt. Also, the Sound Village would likely seek revenge, which could lead to a full - scale war between Konoha and the Sound. Another thing could be that his friends in Konoha might view him differently, some might be afraid of his new - found brutality while others might try to understand his motives.
One possible scenario is that Naruto would gain a lot more knowledge about the village's history and politics. The Sandaime, being an experienced Hokage, could teach Naruto about the different clans in the village, their relationships, and how to manage them. Naruto might also learn more advanced jutsu more quickly, as the Sandaime could give him personal training. This could make Naruto a much stronger ninja at a younger age and perhaps change the course of some of the earlier story arcs.
Well, one possible plot could be that Gato has some new evil plan in the Land of Waves. Naruto, having grown stronger, decides he can't let Gato harm the innocent people there anymore. He uses his new jutsu and his quick thinking to outwit Gato's men first. Then, in a final showdown, Naruto unleashes a powerful Rasengan, directly hitting Gato and killing him, thus saving the Land of Waves from Gato's tyranny.
Naruto would probably be extremely hurt. He has always looked up to the Sandaime as a grandfather figure. So, he might initially go into a state of shock and disbelief.
One common theme could be criticizing the decisions made by the Sandaime Hokage. For example, his handling of the Uchiha situation might be a point of contention in such fanfics. Another theme could be exploring how the village would have developed differently if he hadn't been in power or had made different choices.
In a Ben 10 and Naruto fanfic, there would be some epic battles. Ben's alien forms like Four Arms could have a great brawl with some of the strong Naruto characters like Rock Lee. Four Arms' brute strength against Rock Lee's amazing taijutsu skills would be a sight to see.
If Naruto was the Juubi in the fanfic, there would be a lot of changes. First, his physical abilities would be off the charts. He could probably move at incredible speeds and have superhuman strength. His chakra reserves would be massive, which means he could perform powerful jutsu without getting tired easily. Also, the other characters in the story would probably be in awe or fear of him. His friends might try to help him control this new power, while his enemies would be even more determined to defeat him. It could also change the political situation in the ninja world, as having such a powerful being among them would disrupt the balance of power.