Naruto might initially be shocked. Given his friendly nature towards Sasuke in the original story, he wouldn't expect such an attack from her. So, his first reaction could be pure disbelief.
He could also try to talk to her. Naruto is a character who believes in the power of communication and friendship. He might try to understand why Fem Sasuke is acting this way and reach out to her, even while he's in pain. He might say things like 'Sasuke, we're friends. Why are you doing this?'
In some cases, Naruto could become angry. If the harm done to him is too great, he might abandon his usual pacifist approach for a while. However, this anger would likely be mixed with confusion and hurt. He might vow to make Sasuke understand the wrongness of her actions while also trying to protect himself from further harm.
Naruto would probably be very confused at first. He trusts Sasuke, even if it's a Fem Sasuke in this fanfiction, and he wouldn't expect to be kidnapped by her. So, his initial reaction might be to try and talk to her, asking her why she's doing this.
At first, Naruto would be in disbelief. She has always seen Sasuke as a friend or a rival, not a marriage partner. So, she would likely be very vocal about her opposition. She might gather her friends, like Sakura and Kakashi, to support her cause. She could also try to appeal to Sasuke's sense of justice. Since Sasuke has his own code of ethics, he might also not be happy about this forced situation. Naruto could use this to try and find a way to break free from this unwanted marriage.
At first, Naruto might be extremely shocked. He has always seen Tsunade as a respected figure. So when she hurts him, he may not be able to immediately process it. He could be speechless and just stare at her in disbelief.
Naruto might initially be in shock. He has always idolized his mother, so if she suddenly hurts him, he would be completely taken aback. He might freeze for a moment, unable to believe what is happening.
Naruto might initially be shocked and heartbroken. He may try to hide his pain and put on a brave face, as he has always done in the face of adversity. He could also become withdrawn for a while, distancing himself from Sakura as a form of self - protection.
On the other hand, Naruto could also have some hidden feelings that he wasn't aware of before. So, instead of being angry or shocked, he might start to have a warm feeling inside and start to question his own feelings towards Sasuke.
It could also be due to a power struggle. Fem Sasuke might be jealous of Naruto's growing power and influence. In some fanfictions, characters can be driven by envy, and she might see Naruto as a rival that needs to be put in her place, so she ends up hurting him.
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.
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.
On the other hand, Naruto could also be understanding. If he realizes that Sakura has her reasons, even if they are wrong, he might try to forgive her. Naruto has always been one to see the good in people, and he might hope that they can work through whatever has caused this situation. He may try to talk to her calmly to resolve the issue, showing his maturity and his belief in their friendship.