Well, Sasuke may also feel a sense of betrayal in a way. He's been competing with Naruto all this time, and finding out Naruto is a girl could make him think that Naruto had been hiding something important from him. But at the same time, he may also feel a newfound curiosity about this 'new' Naruto.
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.
Sasuke could be confused at first. His relationship with Naruto has been built on their rivalry and now this new revelation throws everything off balance. He might become more withdrawn as he tries to process this new information and figure out how it changes their dynamic.
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.
Sasuke could also have a complex mix of emotions. On one hand, he has a long - standing relationship with 'Naruto' as a male friend. Now that he knows Naruto is a girl, he might start to feel a different kind of connection. He may become more protective, but also a bit confused about his own feelings towards this new - found knowledge. He might even feel a bit betrayed that Naruto has hidden this fact for so long.
Sasuke would be furious. He's always been protective of Naruto in his own way. He would immediately start looking for her, using all his skills and resources. He might even go on a rampage if he thought Naruto was in serious danger.
Sasuke would be completely shattered. His world would be turned upside down. He had always seen Naruto as a rival, but also as someone important. Naruto sacrificing himself for him would make Sasuke reevaluate his entire life. He would feel an overwhelming sense of guilt and would likely isolate himself from others. However, over time, he would start to use Naruto's sacrifice as a motivation to become a better person and to protect the things Naruto held dear. He would start to follow in Naruto's footsteps in terms of values like friendship and loyalty, and would try to make amends for his past mistakes.
In some cases, Sasuke could be angry. He might see Naruto's request as a sign of weakness or as Naruto giving up too easily. He could lash out at Naruto, telling him to fight instead of asking for death. However, he would still be deeply troubled by the request and would probably struggle with it for a long time, constantly thinking about whether or not he should consider it.
Sasuke might be in shock at first. He can't believe that Naruto is dying in his arms. He may feel a great sense of guilt, thinking that he could have done more to prevent it.
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.
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.
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.
Sasuke would likely first show a stoic exterior when he finds out. However, internally, he's in turmoil. On one hand, he's happy that he and Sakura are going to have a child. On the other hand, he's worried about the potential dangers his family could face because of his past enemies. So, he might start making plans to keep them safe, like finding a more secure place to live.