One possible storyline could be that Ace's death shatters the crew's morale, and Whitebeard, in his attempt to avenge Ace, faces an overwhelming enemy. In the fanfiction, Whitebeard might use his last bit of strength to protect the remaining crew members, leading to his own death. Maybe there could be a flashback of their relationship, how Ace was like a son to Whitebeard and how that bond drove Whitebeard to fight to the end.
In some fanfiction concepts, Luffy could overhear a conversation. Maybe some of the villains are talking about their plans regarding Nami or boasting about how they've been treating her. Luffy, with his excellent hearing skills, picks up on this and figures out that Nami is in a bad situation.
Fanfiction writers often play with the idea of unfulfilled dreams or destinies. Ace and Sabo had so much more they could have done. So, in some fanfics, their memories are so strong that they exist as a sort of spiritual force. And this force is then able to influence events in a way that leads to their physical resurrection. For example, their memories might guide Luffy to a place where he can find the means to bring them back.
For Merlin, there are both good and bad consequences. On the bad side, some of the more traditional and anti - magic people in Camelot might try to oppose him. However, since Arthur now knows, he has a powerful ally. Arthur can protect Merlin from those who would do him harm. Also, Merlin can now be more open about using his magic for the good of Camelot, which is a positive change.
In this type of fanfic, Cass could find out something personal about one of the other characters. Let's say she discovers Tadashi's old dreams that he never got to fully realize. This could lead to a whole new set of interactions within the group, as she might then try to help the others fulfill that dream in some way. It could also show a more emotional side of Cass as she deals with this newfound knowledge.
If everyone found out about Harry's past in fanfiction, there would be a mix of reactions. Some people would probably pity him more, knowing the hardships he had faced before. But others, especially those who were jealous of his fame, might spread rumors or distort the facts. This could also have an impact on how the wizarding community views Dumbledore, as he had been a big part of Harry's past and his decisions related to it.
He would probably be very displeased. Snape has always been strict and traditional, and fanfiction about the DA, which was an unauthorized student group in his eyes, would seem like a frivolous and inappropriate thing to him.
Well, first of all, Luffy is a very emotional character. When he discovers Zoro's sacrifice, he would probably go into a state of shock initially. Then, his reaction could be explosive. He might not be able to accept it right away and would try to find a way to reverse the situation. He could also start blaming himself for not being there to protect Zoro, which would further fuel his determination to become stronger and protect the rest of his crew better in the future.
In some fanfictions, Gwaine might be initially shocked. But given his loyalty to Merlin, he would probably keep the secret. He could also become an ally in Merlin's magical endeavors, using his fighting skills to protect Merlin when his magic is revealed to more dangerous foes.
Well, Percy has seen a lot in his adventures. At first, he might be a bit taken aback because fanfiction is a whole new world compared to his real experiences. However, as he realizes that it's just fans exploring different scenarios with the characters, he could become rather indifferent. He might even start to see the value in it, as it shows how much the fans care about the overall story and its characters. He might think it's a little strange that people are so interested in writing about Nico and Will's relationship, but he'd respect the creativity of the fans.