She could also be amused in some cases. If the fanfiction has some really out - there but harmless ideas about Naruto, like him having a strange hobby that doesn't really change his fundamental good nature, Kushina might find it funny and just shake her head at the creativity of the fanfiction writer.
Well, one scenario could be that Kushina finds a fanfiction where Naruto has turned evil due to some dark force. Another might be that she discovers a story where Naruto is in a relationship that is completely out of character for him. Maybe she stumbles upon a fanfiction where Naruto has some really strange and overpowered abilities that don't fit the original Naruto universe.
In this type of fanfiction, the story could also focus on how the village might react differently to Naruto. Without Kushina's presence, which could potentially have been a positive influence, Naruto might face more hostility. His struggle to fit in and gain acceptance could be more arduous, and this could be what drives him to the brink of insanity. Maybe he would develop a more jaded view of the world and the people in it.
Kushina returning to find crazy Naruto fanfiction could lead to a whole range of reactions. Firstly, she might be appalled at how some fans have twisted the story of her son. On the other hand, she could be amused by the wild ideas. If she finds fanfictions that involve her own backstory in strange ways, she might feel a bit violated but also intrigued. For instance, if there's a fanfiction where her relationship with Minato is completely different from what it really was, she'll have a strong reaction. But overall, it would be a very interesting encounter between her and the world of Naruto fanfiction.
Character development is a major element. As the story progresses, we might see Naruto either getting better or worsening in his insanity, and Kushina evolving in her approach to deal with him. There could also be other characters' reactions to this unusual relationship, which can further shape the story. For instance, Minato's spirit watching over them and how his presence (even if just in memory) affects how Kushina and Naruto interact.
Well, she could start by correcting the out - of - character portrayals. For example, if Naruto is written as overly cruel in the fanfiction, Kushina, as his mother, would know his true kind - hearted nature and rewrite those parts to be more in line with his real personality. She could also fix the plot holes. Maybe in the fanfic, some events don't make sense in the Naruto universe. Kushina, with her knowledge of the world, could fill in those gaps and make the story flow more smoothly. Another thing she could do is to improve the power scaling. If characters are given powers that are way too OP or too weak compared to what they should be in the Naruto series, Kushina could adjust those to make it more believable.
She could be angry if the fanfiction distorts Naruto's character or the story in a negative way. For example, if Naruto is portrayed as a bad person in the fanfiction, Kushina, as his mother, would not like it at all. But if she finds some positive and creative fanfictions, she might be impressed by the fans' imagination.
In this fanfiction, the plot might involve Kushina coming back to help Naruto in his toughest battles. Maybe she uses her unique chakra abilities that Naruto has inherited to give him an edge. She could also provide emotional support, as Naruto has always longed for his mother.
Obviously, Kushina is one of the main characters. Naruto is also a central figure as her son. Since it's related to the Naruto universe, characters like Sasuke, Sakura, Kakashi might also be important in the fanfiction. They could interact with Kushina in various ways, like Sasuke might be skeptical of her at first, or Sakura could be eager to learn from her.
One popular Kushina x insane Naruto fanfiction could be 'A Mother's Love Beyond Reason'. It explores a rather unique take on their relationship where Naruto's insanity leads to some very different interactions with his mother Kushina. It delves deep into how Kushina tries to understand and help Naruto despite his mental state.