No. In the Naruto series, Naruto is the host of the Kyuubi, not its slave. Fanfics might deviate from the original concept, but in the official story, Naruto has a symbiotic relationship with the Kyuubi. He gains power from it and eventually befriends the Kyuubi spirit.
Yes. In many Naruto fanfics, Kyuubi plays a significant role. Since it's so closely tied to Naruto, it can easily be made to serve the fanfic. It might be used to introduce new characters who are interested in the Kyuubi's power. Or perhaps the fanfic is set in a different timeline where the Kyuubi has a different relationship with Naruto and has to serve in a way to protect the village or Naruto himself.
Their relationship could also grow through mutual respect. The female Kyuubi respects Naruto's strength and determination, and Naruto respects her power and the fact that she has been trapped for so long. This respect can lead to a friendship or even something more as they rely on each other more and more in difficult situations.
Well, Kyuubi could help in Naruto fanfic in several ways. It might offer its wisdom to Naruto. Since it has lived for a long time and has seen a great deal, it can give Naruto insights about the history of the ninja world, hidden techniques, or the true nature of certain characters. Also, its presence within Naruto can act as a deterrent to some villains who fear the power of the nine - tailed fox.
One way is by being a power source. For instance, Naruto could draw on Kyuubi's power in new and creative ways in the fanfic. Another way is through its backstory. The fanfic could explore the Kyuubi's past and how it relates to Naruto's present situation, thus serving the plot. Also, Kyuubi could be used as a catalyst for character development, like Naruto learning to better control it and growing as a result.
Well, the Kyuubi might use its chakra to soothe Naruto's emotional pain. It could send warm waves of its powerful chakra through Naruto's body, making him feel more at ease and less heartbroken.
One common way is by sharing its chakra. Naruto can draw on this extra chakra to increase his strength and speed. Another way is through its knowledge. Kyuubi has a long memory and can pass on useful information about the ninja world.
One possible reason could be the loss of a dear friend. Naruto values his friends deeply, and if he were to lose one, it would break his heart. For example, if Sasuke were to die or turn against him completely in a way that Naruto couldn't fix, it would be a huge blow.
Sure. A lot of fan creators are aware that not all fans are interested in adult - themed content. So they write about Naruto and Fem Kyuubi in ways like her being a mentor - like figure to Naruto. This way, it can be a great read for anyone who loves the Naruto franchise.
The theme of redemption can also be common. The fem Kyuubi may have a past that she is trying to overcome, and Naruto helps her in that journey. Also, the exploration of the unknown is a theme. The fem Kyuubi might have secrets about the ninja world that Naruto discovers as they interact more closely.