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.
Often, Poseidon is depicted as heartbroken. He may withdraw from his normal duties and just sit in his underwater palace, watching over Percy's lifeless body or the place where he died. He could also be shown as being very quiet and solemn, his usual boisterous nature gone, replaced by a deep sense of loss.
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.
At first, Percy would likely be angry. He has faced so many challenges with the belief that his father was on his side. The betrayal would make him feel like all his efforts were in vain. He could lash out, perhaps even using his powers in a more reckless way. But as time goes on, he might start to question if there's a deeper reason behind Poseidon's actions and try to find out the truth, especially if he still has friends who believe in him and encourage him to look deeper.
The other sea deities would likely be excited and perhaps a bit envious. Some might offer gifts and blessings for the unborn child. The mermaids and mermen could start preparing grand celebrations in anticipation of the new addition to the underwater royalty.
Paul might be a bit intimidated at first. He's just a mortal, and Poseidon is a powerful god. But he might also be curious. After all, he loves Percy, and Poseidon is Percy's father. So he could start asking questions about Percy's heritage and what it means for Percy's future.
There could also be a situation where Poseidon's family eventually comes around. Maybe his more open - minded relatives see the love between Poseidon and Sally and decide to support them. They could offer their protection and help during the pregnancy. Sally's family, with time, might also learn to accept the situation and be excited about the prospect of having a half - god grandchild or relative.
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.