At first, Naruto could be confused and a bit taken aback. However, his overall positive and accepting nature would soon take over. He might start to think about all the times they trained together and realize that Sasuke's gender never really affected their relationship. He could even joke about it, like 'Haha, Sasuke, I can't believe you fooled me all this time, but it's no big deal!'. And he would continue to see Sasuke as his important friend and rival.
Naruto might be initially shocked. But then he would probably accept it quite quickly because he values Sasuke as a friend above all else. He would likely say something like 'Sasuke, it doesn't matter if you're a girl or a boy, you're still my rival!'.
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.
She would probably be very angry at first. Naruto is a headstrong character, and being kidnapped against her will would make her furious. She'd likely try to fight back immediately, using whatever skills she has at her disposal.
Merlin would probably be heartbroken. He and Arthur have a deep bond, and to have Arthur forget him would be like losing a part of himself. He might initially be in shock and disbelief.
A husband could also choose to distance himself from his wife emotionally. He might start spending more time away from home, either at work or with friends. This is his way of creating a buffer between himself and the painful situation until he decides what to do next. In some cases, this could be a precursor to seeking revenge or payback, like if he starts making new friends who are more successful or attractive than his wife's lover as a way to show her what she's missing.
Some husbands would choose to cut off all communication with the wife and start the process of separation or divorce without much drama, just coldly moving on.
He might be initially confused. Naruto is a character full of energy and he would probably just start blabbing about how he is a boy, not a girl. He could get a bit frustrated as well because Naruto doesn't like being misunderstood.
In some fanfictions, Naruto may become extremely bitter. He could feel a deep sense of betrayal and this might fuel his determination to become stronger, not for the sake of the village at first, but more for self - vindication. He might isolate himself from others and struggle with his identity.
Well, in many such fanfictions, Harry might be shocked at first. He probably feels a sense of pity for Draco too. After all, being under the Imperius Curse means Draco has no control over his actions.
He'd probably be shocked. I mean, Dudley has always seen Harry as the odd one out in the family, and suddenly finding out he's famous in a whole different world of fanfiction would be quite a surprise.
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.