Sasuke might be initially shocked. He has always seen Naruto as a rival and suddenly finding out Naruto is a girl could completely change his perception. He may start to view Naruto in a more protective way, as his traditional views of gender roles might make him feel the need to safeguard her now that he knows she's female.
If Naruto found Kushina alive in a fanfiction, it might lessen his focus on Sasuke for a while. He'd be more centered on getting to know his mother. But in the long run, it could also make him stronger and more determined in his rivalry with Sasuke. With Kushina's support, Naruto would have a new source of motivation to prove himself not just to Sasuke, but also to his mother.
Sasuke would probably be very guarded at first. He's not used to dealing with something so innocent and vulnerable. He might be suspicious of the baby's presence and think it's some sort of trap.
Well, if Sasuke finds out Naruto is a girl in fanfiction, it could completely change their dynamic. Maybe Sasuke would start to see Naruto in a new light, perhaps more protectively. Their relationship might become more romantic as Sasuke realizes his feelings for Naruto are different from what he thought. It could also lead to some interesting plot twists, like Sasuke having to re - evaluate his rivalry with Naruto.
Some characters might be really surprised. Sakura, for instance, might be jealous as she has feelings for Sasuke and now Sasuke might show more interest in Naruto as a girl. Kakashi might be more protective of Naruto, knowing that this new revelation could bring some challenges. And the other ninja in the village could start to treat Naruto differently, either with more respect or in some cases, with unwanted attention.
Naruto may also have to re - evaluate her own identity. She has been living as a boy for so long, and now that Sasuke knows the truth, she may start to question how she wants to present herself in the future. Does she continue to be a ninja in the same way, or does she embrace her femininity more? This could be a major internal struggle for her.
Well, one possible plot could be that Sasuke, being the brooding character he is, is initially confused and a bit irritated by the presence of the baby. But as the story progresses, the baby's innocence starts to thaw his cold heart. Maybe the baby has some special power or connection to Sasuke's past that he discovers over time.
Maybe it's not a trap set by enemies, but rather an old self - defense mechanism of a long - lost village. The cave might be set to protect something precious within, and Naruto's presence accidentally triggered the defenses.
One possible fanfiction could be about Kushina finding Naruto in a situation where he's lost in a forest. Maybe she uses her unique chakra sensing abilities to track him down. It could be a heartwarming story of a mother reuniting with her son.
One possible scenario in this fanfiction could be that Naruto discovers an ancient and mysterious shrine in the forest. The shrine might hold some sort of power or secret. Maybe it has a connection to the Sage of Six Paths. Naruto, being his curious self, would likely start to explore it. He might find strange markings or artifacts inside that he has never seen before.