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.
The Kyuubi often adds an element of mystery and power to Naruto. In fanfictions, this can translate into his relationship with Hinata in various ways. For example, the Kyuubi's power might be seen as something that makes Naruto more worthy of Hinata in the eyes of some characters in the story. Or, the Kyuubi could have a will of its own and actually push Naruto towards Hinata, seeing her as a good influence on Naruto. This can lead to some very unique and engaging story arcs within the fanfiction.
In the fanfiction, Kyuubi could start off as a very self - centered character, only interested in its own power and freedom. But through interactions with Kurama and facing common challenges, it starts to develop a sense of responsibility towards others. Kurama, on the other hand, is initially very reserved. However, as it spends more time with Kyuubi, it begins to open up more and show a more emotional side, like getting angry more easily when Kyuubi makes a particularly dangerous or stupid move.
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.
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.
In fem Kyuubi lemon fanfiction, the gender change of Kyuubi to female brings a different dynamic. Regular Kyuubi fanfiction usually focuses on the male - dominated aspects of the character. But in the fem version, there can be more exploration of femininity, like how she uses her charm or different ways of handling situations compared to the male Kyuubi. Also, the 'lemon' aspect adds a layer of adult - themed content, which is not typically present in regular Kyuubi fanfiction.
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.
One well - written female Kyuubi character could be those who are portrayed as strong - willed. They don't just submit to Naruto but have their own ideas and goals. For example, a character who uses her powers to protect Naruto and the village in her own way, not just following Naruto blindly.