One possible plot could be that Naruto's loss of sanity causes him to have a distorted view of the Fem Kyuubi. Maybe he sees her as both a threat and a source of power he can't control. This could lead to a conflict within himself as he battles his inner demons while also interacting with the Fem Kyuubi in unexpected ways. For example, instead of the usual relationship of cooperation or taming, he might try to completely dominate her, which would be a big shift from the normal Naruto we know.
Perhaps Naruto's loss of sanity is caused by an external force that also affects the Fem Kyuubi. They could be linked in a way that when Naruto starts to lose it, the Fem Kyuubi also experiences some sort of change. This could lead to a situation where they have to figure out how to break free from this external influence together. It might involve them going on a journey through Naruto's mind or some other dimension to find the source of the problem and restore both of their normal states.
Other characters in the Naruto universe might also be affected. For example, his friends like Sakura and Kakashi would notice the change in Naruto. They might try to help him, but their attempts could be in vain because of the complex situation with the Fem Kyuubi involved. This would create new tensions and storylines as they struggle to deal with a Naruto who has lost his sanity and the mystery of the Fem Kyuubi's role in it.
Maybe Orochimaru manages to get his hands on Naruto and subjects him to some dark and twisted experiments. These experiments could mess with Naruto's mind, causing him to lose his sanity. He could start seeing illusions all the time, believing his friends are his enemies. As a result, he'd be in a constant state of confusion and aggression, and his once - positive attitude towards life and ninja - hood would be completely gone.
The fem Kyuubi might feel a sense of protectiveness. Seeing Naruto without his mask could make her realize how vulnerable he is. She may then use her powers to safeguard him from any potential threats that could take advantage of his exposed state.
If Naruto loses his mask in this fanfiction, it might change the power dynamics. His identity being more exposed could make him a target. The fem Kyuubi might have to step up and use her powers to protect him. This could lead to a closer bond between them, and they might start to rely on each other more in the face of new threats.
It could be that Naruto discovers some dark secrets about his past, like his parents were actually killed by the very people he trusted in the village. This revelation is so shocking that it shatters his mental state. He becomes a completely different person, losing his sense of right and wrong, and his sanity along with it.
It could be Kaguya. If Kaguya were to return and use her powerful abilities to drive Naruto mad, perhaps by invading his mind with dark thoughts and memories. She has the power to warp reality and minds, so she could easily make Naruto lose his sanity. And since she has a grudge against the world of ninjas, making Naruto, one of the most powerful ninjas, go insane would be a great way for her to start her reign of terror all over again.
One possible plot could be that the female werewolf is an outcast in her own world. Naruto, with his kind heart, befriends her. Meanwhile, the fem Kyuubi has a connection to Naruto due to the Kyuubi within him. They all come together when a common enemy threatens the Hidden Leaf. The werewolf could use her unique abilities, like enhanced strength and speed, to help Naruto in battles, while the fem Kyuubi might offer her own brand of power, perhaps related to chakra manipulation. As they fight side by side, a deep bond forms between Naruto and the two female characters.
The plot could involve Naruto using his 'godlike' powers to save the fem kyuubi from a powerful threat. Maybe there's an evil force that wants to capture or harm her, and Naruto steps in.
Well, it could be about Naruto having a unique relationship with a female Kyuubi who has been banished. Maybe Naruto tries to find a way to bring her back and in the process, they develop deep emotional bonds. He might face many challenges, like opposition from the village or other powerful forces who don't want the Kyuubi back.
Well, it could be about the cryomancer Naruto using his ice powers in unique ways while interacting with the female Kyuubi. Maybe they team up to fight some common enemies, or there could be a story of them falling in love and trying to overcome the differences between a human - like Naruto and a more mythical being like the fem Kyuubi.