A more complex plot could involve the 'knotting' as a way to merge their powers in a new and unexpected way. This new power attracts the attention of other villages or dark forces. Naruto and the female Kyuubi then have to navigate the political and dangerous situations that arise, all while exploring their relationship which is evolving due to the 'knotting'.
I'm not entirely sure as I haven't read that specific fanfiction. But generally, in Naruto fanfiction, a 'Naruto x Fem Kyuubi' might explore a romantic or unique relationship between Naruto and a female version of the Kyuubi. However, the 'lemon' part often implies some form of adult or sexual content, which is not suitable for in - depth discussion here.
One popular plot could be their adventures together in the Naruto world. For example, they team up to face a new and powerful enemy that neither Naruto nor the fem Kyuubi could defeat alone. They learn to combine their powers in unique ways, like the fem Kyuubi lending her chakra in a more controlled manner to Naruto, allowing him to access new jutsu forms.
In 'Naruto x Female Kyuubi' fanfiction, the romance can be quite interesting. Usually, it might involve Naruto seeing the female Kyuubi in a new light. He could start to understand her better beyond just being the nine - tailed beast. Their relationship might develop as they face common enemies together or during Naruto's training sessions where he has to interact more closely with the Kyuubi's power which is now in a female form.
You can start by looking on fanfiction websites such as Archive of Our Own (AO3). There are often specific tags for different pairings like 'female Naruto' and 'female Kyuubi'. Many authors explore this unique pairing there, and you can filter the results to find exactly what you're interested in.
The unique dynamic between them. Female Naruto would likely have a different kind of connection with a female Kyuubi compared to the original male Naruto and Kyuubi relationship. It could explore new aspects of friendship, power sharing, or even a romantic relationship in a fresh way.
One great fanfiction could be 'The Bond of Female Naruto and Kyuubi'. It delves into how a female Naruto might form a unique relationship with the Kyuubi. In this story, the female Naruto has a more empathetic connection with the Kyuubi, understanding its loneliness. Another one is 'Female Naruto's Kyuubi Adventure' which focuses on their joint adventures, with the Kyuubi lending its power to the female Naruto in a more nuanced way compared to the original series.
In the fanfiction, the female Kyuubi could be reincarnated into a human form. Naruto, being the only one who knows her true identity, has to protect her from those who would harm her. Anko gets involved when she notices Naruto's strange behavior. As they try to keep the female Kyuubi's identity a secret, they end up in a series of comical and dangerous situations. Eventually, they all become good friends and work together to fight against a common enemy that threatens the safety of their village.
It could be an original character created by the fanfiction author. This character might be a descendant of the original Kyuubi, but with a female form and her own distinct personality.