Well, Anna would be frantic. She'd immediately set out to find Elsa, not caring about the danger. She might even team up with the Guardians without hesitation. Kristoff would be right by Anna's side, using his survival skills to try and track down Pitch's location. Olaf, being the innocent and loving character he is, would be heartbroken. He might try to cheer Elsa up from afar by singing or reminiscing about their good times, hoping it reached her somehow. The trolls, if they found out, would offer their wisdom and perhaps some magical aid to help in the rescue of Elsa from Pitch's clutches.
Well, there are also those characters who might be a bit shocked or confused. Take Levi from Attack on Titan. He's a very serious and no - nonsense type of character. If he were to read some of the fanfic about him that deviated too much from his own self - perception, like being made into a comical or overly emotional character in the fanfic, he might be taken aback at first. But then he might also realize it's just a different interpretation and not take it too seriously.
Obviously, Elsa is one of the main characters. But without reading the novel, it's hard to say who else might be important. There could be a guide character who helps Elsa on the island.
The people of Arendelle would be in a state of chaos and mourning. Elsa has been their queen and their protector. Some might be afraid that without Elsa, the kingdom would be vulnerable to new threats. The trolls, who have known Elsa since she was a child, would also be deeply saddened. They might try to find a way to bring her back, using their own magic and knowledge. Sven, Kristoff's reindeer, would sense the change in Kristoff's mood and would be more subdued, staying close to his owner during this difficult time.
Elsa's reaction would be complex. She has spent most of her life in isolation, fearing her own powers. A kiss from Hans would be something she never expected. She might feel a sense of betrayal towards her sister Anna at first, since Hans had once tried to harm Anna. But as she realizes her own feelings, she would have to face her inner demons. Hans would be elated at first, but then he would quickly realize that he has a long way to go to earn Elsa's trust. He would need to prove that he is a changed man, and the kiss would be the start of that journey of proving himself.
Well, it depends on the nature of the fanfiction. Some anime characters might be amused if the fanfiction is light - hearted and full of comical situations. For example, if it's a fanfic about a cooking competition among the characters from a shonen anime, they might react with good - natured laughter and competitiveness. They could also be confused if the fanfiction takes their story in a very strange or unexpected direction, like suddenly making a character from a historical anime end up in a space adventure.
Kakashi would be very observant. He would look for how the fanfiction writers understand the world of Naruto, the values and the moral lessons. He might even use some of the creative ideas from the fanfiction in his own teachings if he thought they were valuable and in line with the spirit of the original story.
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.
They might be confused at first. RWBY has its own unique lore and concepts that are different from many anime. So anime characters may need time to understand things like Grimm and Huntsmen. For example, if Goku from Dragon Ball was watching, he'd probably be like 'What are these strange monsters?'.
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.