Well, the idea of a 'naruto gets betrayed by natasha fanfic' is quite an interesting crossover concept. Since Naruto is from the Naruto anime/manga world and Natasha is from the Marvel universe. It's possible that such a fanfic might be exploring the idea of how Naruto, who is used to his own set of values and relationships in his world, would react to being betrayed by Natasha. However, as I said before, actually finding it would require some in - depth searching on the appropriate fanfic platforms and communities.
Maybe Natasha, in this fanfic, could be working undercover among Naruto's group for some secret mission. She gains Naruto's trust over time, but then reveals her true motives which are against Naruto's goals, thus betraying him.
Another plot could involve jealousy. If Sakura becomes jealous of Naruto's growing popularity and power among the villagers, she might betray him. She could spread false rumors about him, which would lead to the villagers turning against Naruto.
In such a fanfic, the plot might start with Naruto's friends gradually turning against him due to false rumors spread by a hidden enemy. They could start to exclude him from missions and isolate him within the village. For example, Sasuke might believe the lies and challenge Naruto, thinking he has changed for the worse. This would lead to a series of battles where Naruto has to fight not only his former friends but also his own feelings of betrayal and confusion.
The betrayal could lead to Naruto having trust issues not only with Sakura but also with others in the future. He might become more guarded and less likely to open up to people. For Sakura, if she comes to her senses later, she would have to face the enormity of what she has done. She would have to grovel for Naruto's forgiveness, but it would be a long and difficult road to regain his trust.
The main antagonist might be an organization that wants to take over the Hidden Leaf Village. They see Naruto as a major obstacle because of his strength and influence among the villagers. So, they devise a plan to make everyone in the village betray Naruto. They use mind - control techniques or spread misinformation on a large scale to achieve their goal. This way, they can weaken the village from within before making their move to take it over.
One possible plot could be that Naruto discovers his friends have been secretly working with an enemy. They might have been promised power or something valuable in return for betraying Naruto. Maybe they spread false rumors about Naruto, turning the village against him.
Naruto would likely become more distrustful at first. He's always been so open and trusting of his friends, so this betrayal would shatter that. He might become more withdrawn, constantly second - guessing people's motives.
In the '4 kunoichi gets betrayed fanfic', it could be that the four kunoichi are working for a noble cause. However, one of their own, due to jealousy of the attention the others get, decides to betray them. She spreads false rumors about them, making the whole ninja community turn against them. The four kunoichi have to prove their innocence and also figure out a way to deal with the traitor within their group.
It could be their master. Maybe the master has been corrupted by dark forces. He sees the potential in the kunoichi and fears they will become more powerful than him. So, he betrays them to stop their progress.