Well, it could mean that this fanfiction was one of the first to explore Naruto's relationship with the Kyuubi. Maybe it delved into how Naruto's life was affected by having the Kyuubi sealed within him in a unique way that hadn't been done before in other works.
I'm sorry, without actually reading the fanfiction, it's hard to say exactly what the plot is. But generally, it might be about Naruto's life with the Kyuubi. It could involve his struggles, his growth, and how he copes with having such a powerful and dangerous entity within him.
At first, Naruto might be scared or wary of Fem Kyuubi. But as time passes, he starts to see her as a protector. She teaches him about his own power and the secrets of the chakra. Their relationship becomes more of a student - teacher one. Then gradually, it turns into a deep bond like a mother - son relationship. Fem Kyuubi starts to care for Naruto not just as a vessel but as a person she has a connection with.
One great fanfic in this genre is 'Naruto: Time - Travel with the Female Kyuubi'. It has an interesting plot where Naruto and the female Kyuubi travel back in time and have to deal with past threats in new ways. The character development is really well - done as Naruto learns to rely on the female Kyuubi's unique powers and perspective.
The fem Kyuubi could have more delicate features compared to the traditional, more menacing Kyuubi. For example, her eyes might be more almond - shaped and have a softer glow. Her fur could also be a different shade, perhaps a lighter red or with some kind of pattern on it.
One common theme is self - discovery. When Naruto becomes the Kyuubi and travels through time, he often has to re - evaluate who he is. For example, he may see how his actions in the past could have different consequences than he thought.
Maybe it's because Naruto has some sort of special connection or resemblance to the Kyuubi that Kushina notices. For example, Naruto might display some of the Kyuubi's power characteristics in an obvious way that makes Kushina jump to that conclusion.
At first, Naruto might see the Kyuubi as just a source of power. But as he starts to protect it, he realizes it's more of a partner. Their relationship evolves from a simple user - power source dynamic to a deep - seated friendship. He begins to understand the Kyuubi's emotions and past, which further cements their bond.
Sasuke is often a popular character in these fanfictions. His relationship with Naruto can be further explored in the context of the Kyuubi's fatherly influence. Maybe Sasuke is initially skeptical of this new - found bond between Naruto and the Kyuubi but later comes to accept it. Sakura is also a common character. She might notice the changes in Naruto due to the Kyuubi's fatherly presence and be either supportive or a bit jealous. Kakashi could also be there. He might be observing Naruto's growth under the Kyuubi's guidance and offer his own wisdom as Naruto's former teacher.
In this fanfiction, their relationship becomes more of a partnership. Instead of Naruto just using the Kyuubi's power, they work together as brothers. Naruto might start to understand the Kyuubi's feelings and motives better.