Sasuke would likely be a bit stunned at first. He's a complex character. But then he would become very protective. He has lost so much in his life, and he wouldn't want to lose Sakura or the baby. He might become more vigilant and even cut back on some of his more dangerous missions.
There might be a fanfic named 'Hidden Torments'. In this, Sakura's family secrets could be the source of her dark past. For example, her family might have been involved in some sort of ninja - related scandal that she has to bear the burden of, and Sasuke gradually helps her uncover and deal with it as their relationship develops.
Sasuke might initially be shocked. He has always seen Sakura as someone connected to Konoha, so her leaving would be unexpected. He could be concerned about her safety, especially if she leaves without proper preparation or protection.
The fanfic can use the reactions of other characters. If Sasuke starts to notice Sakura's strange behavior when certain topics are brought up, like her flinching when someone mentions a particular mission. His curiosity can then lead to the discovery of her dark past. Also, the use of her internal monologue can be very effective. She can constantly be thinking about her past mistakes or traumas, like how she might have let someone down during a critical moment in her past.
He would probably be quite amused by some of his past antics. For example, his constant pranks on Iruka-sensei. But at the same time, he'd also see the pain he carried from not having his parents and realize how that influenced his actions. He might react with a bit of regret for some of the stupid things he did out of loneliness, but also be glad that those experiences made him who he is today.
Anti Sasusaku fanfic focuses on going against the Sasusaku relationship. So, while regular Sasusaku fanfic might show the growth and love between Sasuke and Sakura, anti ones would show the opposite. For example, they could show Sasuke constantly rejecting Sakura or having a negative view of her.
Well, some past gods might be amused. They'd see these modern interpretations of their stories and characters in the Percy Jackson fanfiction as a strange yet interesting new form of worship or at least attention. For example, Zeus might be a bit irked at some of the liberties taken with his character, but also secretly flattered that people are still so interested in him.
Captain America would probably be very reflective. He might see his past self as a reminder of his long journey and how much he has changed. He could try to offer some words of wisdom to his younger self.
The popularity also stems from the fact that Sasuke and Sakura are well - known characters from a very popular anime/manga. People are already invested in them, so they are eager to read fictions that focus on their relationship, whether it's about their love, friendship, or their journey together.
Well, Boruto could be very inspired. Naruto's past is full of struggles, from not having parents around to being constantly underestimated. When Boruto discovers this in the fanfiction, he might realize that his own problems are not as big as he thought. He could be motivated to work harder and not take for granted the things he has, seeing how much Naruto had to fight for everything.