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.
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.
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 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.
Minato is often paired with Kushina in these fanfictions. Their relationship was a significant part of the Naruto story, so many fanfictions expand on their love story. Another popular pairing is Kushina and Naruto. It could be a story where Kushina is brought back to life and gets to be a part of Naruto's life in a more direct way.
One possible plotline could be Kushina's reunion with Naruto and how she uses her skills and wisdom to help him in his battles. For example, she might teach him some new jutsu that only she knew. Another plotline could involve Kushina exploring the new ninja world that has changed so much since her time. She could interact with characters like Sasuke and Sakura, and have an impact on their development as well.
One interesting fanfiction could be about Kushina's untold adventures before Naruto was born. Maybe she had some secret missions that involved protecting a powerful artifact. Another could be a story where Kushina gets to train Naruto in some special and unique jutsu that only she knew. And there might be a fanfic where Kushina interacts with characters from other villages in a way that changes the whole Naruto storyline.
Sasuke might be affected as Naruto's closest friend. With Kushina back, Naruto could be more at peace, which might change the dynamic of their relationship. Sasuke could see a different side of Naruto, one that is more complete with his mother's presence.