He might be initially confused. Naruto is used to dealing with all kinds of opponents and situations, but a yandere Kyuubi would be a new and strange thing for him. He could try to reason with her at first.
At first, Naruto would probably be quite oblivious to the yandere tendencies of the female Kyuubi. He's so focused on his goals like becoming Hokage and protecting the village. But as things start to get out of hand, like if she starts to isolate him, he would start to resist. He values his relationships with his friends and his village, and he wouldn't let her yandere behavior disrupt all that. He might even try to find a way to cure her of her yandere - like behavior if possible, because Naruto always tries to see the good in people and help them.
Well, the plot could involve the female Kyuubi being overly possessive of Naruto. Maybe she tries to keep him away from his friends and training, seeing them as threats to her relationship with Naruto. She might use her powers to intimidate anyone who gets too close to Naruto.
Naruto might be really confused at first. He's used to people being friendly or having normal crushes, but a yandere is a whole different level. He'd probably try to talk to her and understand why she's acting so strangely.
One common theme is the unbalanced power dynamic. Since the Kyuubi is a very powerful being, when she is in a yandere state towards Naruto, her power can be both a protection and a threat to him. Another theme is the idea of obsessive love. The yandere fem Kyuubi often shows an all - consuming love for Naruto that goes beyond normal boundaries.
Naruto would probably be really confused at first. He's used to a loving mother figure, not a yandere one. He might try to talk to her and understand why she's acting so strangely.
Naruto might be initially confused. He's used to people being friendly or at least straightforward with their intentions. So when Mikoto starts showing her yandere side, like getting overly possessive, Naruto would probably be like 'What's going on?'. He could try to talk to her and understand her behavior at first.
At first, Naruto might be really confused. He's used to the normal Sakura, so when she starts acting all yandere, he'd be like 'What's going on, Sakura - chan?'. He'd probably try to talk to her and find out what's wrong.
Naruto might also feel a sense of responsibility. He might think that he did something to cause Yugito to act this way. So he could start to limit his own actions to avoid triggering her yandere behavior. For instance, he might stop being so friendly with other girls in front of her. But at the same time, he would not give up his own dreams and values, and would try to make Yugito understand that her behavior is not acceptable in a way that is both firm and kind.
Naruto might initially be shocked and angry. He has always considered the Kyuubi as an enemy within him, and now being kidnapped by it is the worst - case scenario for him. He could try to fight back immediately, using whatever little chakra he can muster without relying on the Kyuubi's power.
If the female clone's actions become more extreme, Naruto would likely become more serious. He has a strong sense of justice and protecting his friends. He wouldn't let her harm anyone. He might try to use his own ninja skills to subdue her and figure out a way to reverse whatever made her this way. He'd also draw on his own experiences of being an outcast and try to reach out to her on an emotional level, hoping to change her yandere ways.
Obviously, Naruto and the yandere fem Kyuubi are the main characters. Naruto is the protagonist of the Naruto series, and in this fanfiction, he becomes the focus of the yandere fem Kyuubi's affections.