One possibility could be a misunderstanding. Maybe Kakashi is framed for something that makes Naruto believe he has betrayed him. For example, an enemy could use a clone of Kakashi to perform a heinous act, and Naruto witnesses it without seeing the full picture.
Another plot could involve mind control. An evil force might gain control over Kakashi's mind, forcing him to act against Naruto. This would create a tragic situation where Kakashi has no control over his actions, and Naruto is left heartbroken and confused, thinking his mentor has turned on him.
However, Naruto also has a big heart. In the long run, he would probably try to find a way to save Kakashi or bring him back to the right side. He wouldn't give up on Kakashi easily, believing that there must be some underlying reason for his actions and that he can be redeemed.
One possible plot could be that Naruto discovers some dark secrets about Konoha's leadership. For example, he might find out that they were involved in unethical experiments in the past. This discovery could make him feel betrayed first, and then lead him to take actions that Konoha sees as betrayal, like refusing to follow orders or even teaming up with an enemy of Konoha who he believes has a more just cause.
One possible reason could be power. Maybe in the fanfic, there's a new source of power that Tsunade wants desperately and Naruto stands in her way to obtain it. So she betrays him to get to that power.
At first, Naruto would likely be extremely shocked. He has always considered Sakura a friend and teammate, so this would be a huge blow. He might question his own judgment in trusting her.
One possible plot could be a power struggle. Maybe in a world where different fictional universes collide, Naruto God represents a certain power balance. Wonder Woman, perhaps influenced by some external dark force or a misunderstanding of Naruto God's intentions, decides to betray. This could lead to epic battles between their respective allies, with the fate of this combined fictional universe at stake.
Another aspect could be related to her past or origin. If she has some hidden memories or a secret agenda tied to her existence as the Fem Kyubii, it could lead her to betray Naruto. For example, if there are some dark forces that are controlling or influencing her from her past, she may be forced to turn against Naruto against her will in a sense.
Maybe Naruto has discovered a new powerful jutsu that Kakashi isn't aware of. This gives him an edge in the fight and he manages to defeat Kakashi.
One possible plot could be that Kakashi trains Naruto in a more personalized way. He might share his own experiences more deeply, like his time with Obito and Rin. Naruto could also pick up some of Kakashi's laid - back attitude while still maintaining his own energetic self. Kakashi would probably be more protective, which could lead to some interesting interactions with the other villagers who used to shun Naruto.
A possible plot could be that in a mission gone wrong, Naruto and Kakashi get separated from the rest of the team. They end up in a strange place where they have to rely on each other more than ever. As they face various challenges together, their bond deepens and Naruto realizes his feelings for Kakashi, leading to a kiss.
The plot could be that Naruto gets a special mission to protect Kakashi's face from a group of rogue ninjas who want to steal Kakashi's identity. Naruto has to use his unique skills to fend off the attackers and keep Kakashi's face safe.