If the Kyuubi loses its memory in the fanfiction, it could potentially change the entire Naruto storyline. For instance, Naruto may no longer have the same source of power that he once had. Instead, he might have to rely on his own natural talents and training more than ever. The Kyuubi, without its memories, could start to develop a new personality. It might become more curious and innocent, which would be a huge contrast to its previous menacing self. This would force Naruto to adapt and also give the other characters in the series new ways to interact with both Naruto and the Kyuubi.
Perhaps the Kyuubi's memory loss reveals a hidden side of its power. Without the memories that were holding it back in a certain way, it could unlock a new and even more dangerous form of power. This could put Naruto in a difficult position as he tries to control or understand this new aspect of the Kyuubi. Also, a plot twist could be that the Kyuubi's memory loss is contagious, and it starts to affect other tailed beasts in the Naruto universe, leading to a whole new set of problems for the ninja world.
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.
A 'Naruto loses his memory fanfiction' might involve a mysterious curse placed on Naruto. He forgets not only his personal relationships but also his ninja skills. His sensei, Kakashi, could take it upon himself to reteach Naruto everything from the basics. Meanwhile, Naruto might form new, unexpected relationships with people in the village who don't know the 'old' him, and these new relationships could either help or hinder his journey to regain his memory.
It could be Orochimaru. He's always been interested in Naruto's power. Maybe he devises a plan to make Naruto lose his memory so he can manipulate him more easily, perhaps to use him as a weapon against the Hidden Leaf.
Well, he could start making really rash decisions. Maybe he'd attack his friends by mistake, thinking they were enemies. Since he's lost his mind, his usual judgment would be out the window.
In such a scenario, his relationships would be severely affected. His friends would be horrified by the change in him. Naruto's bond with Sasuke, for example, would be in jeopardy. Since he has lost his humanity, he may not understand the concept of friendship anymore and might even see Sasuke as a rival to be eliminated. And his relationship with the female Kyuubi would be complex. Maybe she would try to control him or use his new state for her own purposes.
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.
The storyline might start with Naruto being put in a really difficult situation that causes him to lose his mind. Then, the female Kyuubi could be introduced as a key factor in his recovery. Maybe she has some special ability or knowledge that can help him get better.
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.
One great fanfiction with this theme is 'Fading Memories'. It beautifully explores Draco's struggle as he loses his memory and how it affects his relationship with Harry. The story is full of emotional moments and really delves deep into their characters.