A frequent theme is the transformation of their relationship. At first, it could be a relationship based on fear or mistrust. But as the story progresses in the fanfiction, it can turn into a deep friendship or even a romantic relationship. There is also the theme of redemption in some cases. Maybe the female Kyuubi has some past deeds that she wants to make up for, and Naruto helps her in that journey.
Power and control are often themes. The female Kyuubi has great power, and Naruto has his own power and his experience with the original Kyuubi. So, in fanfiction, there could be a struggle or a cooperation regarding who has control over what. Also, the theme of acceptance. Naruto has to accept this new form of the Kyuubi, and the Kyuubi might have to accept Naruto's way of doing things.
Well, often there's the theme of acceptance. Naruto has to accept the female Kyuubi (if it's in a form where it's a character) and the other girls in the harem. And the girls also have to accept Naruto with all his flaws and his connection to the Kyuubi. There's also the theme of adventure. They go on adventures together, exploring new parts of the Naruto world, and in the process, their relationships deepen.
One common theme could be power struggle. Since Naruto is evil, he might be misusing the power of the Kyuubi in a more malevolent way compared to his normal self. Another theme could be redemption. Despite being evil at first, there could be a journey towards redemption through his interactions with the female Kyuubi. Also, there could be a theme of forbidden love. Their relationship in this fanfiction could be something that goes against the norms of the Naruto universe, adding an element of drama.
Power and its consequences is also a major theme. Having Kitsune and Kyuubi powers can be a double - edged sword. She can use them for great good, like protecting the village, but she also has to deal with the negative aspects. People might be afraid of her or try to use her powers for their own evil purposes. This is often explored in these fanfictions. In some stories, she has to learn to control her powers so that they don't consume her.
One common theme is power. How Naruto's connection to the Kyuubi gives him extraordinary abilities. Another is identity, as he has to figure out where he ends and the Kyuubi begins.
One common theme is the power struggle. It often shows Naruto trying to control the Kyuubi's power, which can be overwhelming at times. Another theme is friendship. Despite the initial hostility between Naruto and the Kyuubi, many fanfictions explore how they can become friends or at least allies.
A common theme is the relationship development between the sub female Kyuubi and Naruto. It often involves the exploration of their unique bond, perhaps starting from a place of misunderstanding and growing into something deeper.
One common theme is the power dynamic. Naruto has his own strength, but the female Kyuubi brings a whole new level of power. Their relationship might explore how they balance that. Another theme could be acceptance. Naruto has to accept this new, feminized version of the Kyuubi, and she has to accept him as her partner in a sense. Also, there's often the theme of redemption, as the Kyuubi was once a feared entity, and through their love, she could find a new path.
Well, a frequent theme is probably the impact on the Naruto world as a whole. How does the news of a female Kyuubi being pregnant affect the balance of power? Also, there could be themes centered around the emotional journey of Naruto and the female Kyuubi. They might have to deal with their own feelings towards each other, and towards the unborn child. Additionally, some fanfictions may focus on the mystery of how this pregnancy even occurred in the first place, given the unique nature of the Kyuubi.
Another theme is identity. The female Kyuubi may not know who she really is or where she comes from. She could be on a quest to discover her true nature. This can involve exploring her past, her relationship with other characters, and how she fits into the world around her. It can be a very self - discovery - heavy theme.
Power control is a very common theme. Writers often explore how Naruto gains better control over the Kyuubi's power, whether it's through new training methods or emotional breakthroughs. Another common theme is the reaction of other characters. How do Sasuke, Sakura, and the other villagers respond to Naruto's new and sometimes terrifying form? It can range from fear to admiration.