One interesting plot could be Naruto using his unique bond with Kyuubi to help it regain its lost memories. Naruto might explore the Kyuubi's past and discover things that even the Kyuubi itself had forgotten. This could lead to new powers or a deeper understanding between them.
Another plot could involve Naruto helping Kyuubi to control its power better. Since Naruto has experience in taming the Kyuubi's power within him, he could teach the Kyuubi some techniques or mental exercises. For example, Naruto could show Kyuubi how to focus its chakra in a more refined way, which in turn could make Kyuubi more powerful and less of a threat to the world. In this way, they could form an even stronger partnership.
A possible plot is that Naruto helps Kyuubi to communicate with other tailed beasts. As Naruto has connections with the other Jinchuriki and has some understanding of the tailed beasts, he could act as a mediator. He could help Kyuubi to convey its thoughts and feelings to the other tailed beasts, which might lead to a new alliance among the tailed beasts and change the power dynamics in the Naruto universe.
In some fanfictions, the Kyuubi's protection might lead to Naruto having a special bond with nature. Since the Kyuubi is a powerful force, it could influence Naruto's chakra in a way that makes him more attuned to the natural elements around him. This could give him an edge in battles, like being able to manipulate the environment in ways others can't.
One interesting plot could be the Kyuubi's influence on Naruto's relationships in the harem. For example, the Kyuubi's power might attract some characters who are interested in that power, leading to unique interactions. Another plot could be Naruto having to balance his newfound harem with his ninja duties, and the Kyuubi sometimes interfering or helping in these situations.
Another plot could be Kyuubi teaching Naruto some ancient and forgotten ninja techniques. As a powerful and ancient being, Kyuubi might know some techniques that have been lost over time. Naruto could then use these new techniques to surprise his opponents in battles and also contribute to the growth of the ninja arts in the village.
One interesting plot could be Naruto learning to control the Kyuubi's power in unique ways that are different from the original story. For example, he might be able to use the Kyuubi's chakra to create new jutsu that are a combination of his own skills and the Kyuubi's raw power.
One possible plot could be Naruto gradually realizing his feelings for Fem Kyuubi as they go through various adventures together. Maybe they start off as friends but as they face more and more challenges, like fighting powerful enemies, their bond deepens into love.
One possible plot could be that the Kyuubi's chakra constantly overwhelms Naruto's mind, leading him to make rash decisions in battles. For example, he might attack his allies by mistake when the insanity takes over.
In some naruto x girl kyuubi fanfiction, the plot might revolve around the girl being an outcast because of her Kyuubi - like powers. Naruto, who has always been an outcast himself, helps her accept herself. They then train together to master their powers and become a formidable duo in the ninja world. This could also lead to a romantic relationship as they understand each other on a very deep level.
In a female Naruto fox Kyuubi fanfiction, a great plot could be her having to prove herself to the village. Since she's female and has this connection to the Kyuubi, some villagers might be more skeptical or even afraid of her. She then has to go on a journey to show that she can control the Kyuubi's power and use it for good. Along the way, she meets other characters who either help or hinder her progress. And she might also discover secrets about the Kyuubi's origin that no one in the village knew before.
One possible interesting plot could be Naruto and Kyuubi forming an unexpected bond despite the slave - like relationship. Naruto might gradually understand Kyuubi's pain and try to free it in a unique way.
In some fanfictions of this type, an interesting plot could be the transformation of the harem due to Naruto's growth and new powers related to the Kyuubi. As Naruto becomes stronger, the dynamics within the harem change. New characters might be attracted, and old relationships might be re - evaluated. This could create a complex web of emotions and storylines that keep readers engaged.