There are those characters who would be angry or offended. If the fanfiction portrays them in a bad way or changes their relationships in an unflattering manner, they would likely not be happy about it. For instance, a heroic character being shown as a villain in the fanfiction. They may try to stop the spread of such fanfiction.
Some characters might be amused. They could find the different interpretations in the fanfiction entertaining and might even share it with other characters.
Other characters could be confused. Since they are used to their own story as it is in the original work, seeing a different version in the fanfiction might make their heads spin. They may start to question the reality of their own story and what really defines them as characters.
They could be surprised. The fanfiction might show them in scenarios they never imagined, like a shy character being in a very bold and adventurous situation.
Some characters might be excited. They could be interested in seeing how their story continues in the fanfiction. Others might be skeptical and think that the fanfiction is not a true representation of their possible futures.
Some characters might be angry if the fanfic misrepresents them completely. For instance, if a heroic character is made into a villain in the fanfic, they would surely not be happy about it.
Some members like Itachi might be very calm and just observe quietly. He would probably analyze the stories, thinking about how the characters are developed and what the underlying themes are.
Some characters might be critical. Elsa, being a powerful and responsible character, might not like it if the fanfiction misrepresents her in a way that goes against her values. She might think that the writers should be more respectful of her character arc and not make her do things that are completely out of character just for the sake of a wild story. However, at the same time, she might also appreciate the creativity in some parts.
Some would be intrigued. Captain America, being an open - minded person, might be interested in seeing different interpretations of their team dynamics. He could even gain new insights about his relationships with his fellow Avengers through the fanfiction.
Characters might also be a bit critical. They know their world and themselves better than the fanfiction writers. So they could be nitpicking at inaccuracies or things that don't quite fit with their personalities. But at the same time, they may also be impressed by the creativity and passion that goes into creating these fanfictions.
There could be characters who are outraged. If the fanfiction distorts their personality or makes them do things completely against their nature, they may be very angry. For example, a noble character made to act like a coward in the fanfiction would likely not take it well.
Characters may have different reactions. For example, if a character is normally shy in their original story but the fanfiction portrays them as a bold adventurer, they might be initially taken aback. But then they could start to think about that different side of themselves. Or if a character is a villain in the original and the fanfiction gives them a redemption arc, they might feel a sense of hope or confusion about this new view of themselves. They may also get excited to see new plotlines and relationships that fans come up with.
When characters watch reviews, they may experience a range of emotions. A character who is insecure might be deeply affected by negative reviews and might even question their own worth or actions within the story. In the case of fanfiction, they could be in awe of the fans' imagination. They might see new possibilities for their own character development that they hadn't considered before. However, they could also be very protective of their original story and not like some of the liberties taken in the fanfiction.