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.
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.
There would also be some fans who might be a bit shocked. Naruto and Sasuke's relationship has always been complex and more of a deep friendship/brotherly bond in the original series. So a kiss might seem a bit out of character to them at first. But for those who love exploring different interpretations, they might come around to it and start to enjoy the new take on their relationship.
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.
One possibility is that it could lead to a major shift in their relationship. They might start to question their feelings towards each other more deeply. Maybe Naruto becomes more confused about his friendship with Sasuke as this unexpected kiss has added a new layer of complexity.
He may also choose to defend himself without really fighting back. Naruto values Sakura as a friend and teammate, so he would be reluctant to harm her. He might just try to dodge her attacks and keep talking to her, hoping to snap her out of it.
Well, Naruto might be furious. He's always been protective of Sakura. He'd probably drop everything he's doing and go after Sasuke to rescue Sakura. Naruto has a strong sense of justice and loyalty, especially towards his friends. And Sakura is one of his closest friends, so he won't stand by and let her be in danger.
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.
In this fanfiction, the act of Sasuke kissing Naruto's neck might be a turning point. It could make Naruto more aware of Sasuke's emotions towards him. Maybe Naruto has always been a bit oblivious to Sasuke's deeper feelings. This moment forces him to confront and evaluate their relationship. For Sasuke, it could be a way of finally expressing himself after holding back for so long. This exchange then paves the way for them to communicate more openly about their relationship and move towards a closer, more trusting connection.
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.