At first, Sasuke would be filled with rage. His Sharingan was something he had cultivated and was a symbol of his Uchiha heritage. Naruto stealing it would be like stealing his very soul. He would immediately try to hunt Naruto down. But as he chases Naruto, he might start to think about the reasons why Naruto did it. He could consider if there was some greater threat that Naruto was trying to combat, but still, he would not be able to forgive Naruto easily and would demand his eyes back.
Yes, it can be a somewhat popular trope in the Naruto fanfiction world. Some fans like to explore alternative relationship dynamics. They might be interested in seeing how Naruto's relationship with Sakura could develop in a scenario where he 'steals' her from Sasuke. It adds an element of drama and can lead to interesting character development as Naruto might have to overcome his own feelings, Sakura's prior attachment to Sasuke, and Sasuke's reaction if such a thing were to hypothetically happen.
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.
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.
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.
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.
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.
The Uzumaki family might be a bit shocked at first. But Naruto's kind - hearted nature could make them eventually come around. His mother Kushina might be more accepting as she always wanted Naruto to be happy. As for Sasuke's family, well, it's a bit more complicated. Since Sasuke is the last of the Uchiha, his family's traditional values might be a hurdle. However, if Sasuke is determined, he might be able to convince any remaining family members or those who care about the Uchiha legacy that his relationship with Naruto is a positive thing.
Sakura would be devastated. She has deep feelings for both Naruto and Sasuke. She might turn against Sasuke completely and try to take revenge herself. Kakashi would be in shock. He has mentored both and would likely feel like he failed in some way. As for the other ninja from the Hidden Leaf, they would be angry and mournful at the loss of their hero Naruto.