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.
Percy's reaction would be complex. He would be devastated, of course. His trust in his father has been a cornerstone of his identity. He might isolate himself from his friends for a while, feeling like he can't trust anyone. However, his loyalty to his friends and his sense of justice would eventually kick in. He would start to investigate why Poseidon betrayed him. He might also struggle with his own powers, as they are a gift from Poseidon, and wonder if he can still use them without being under his father's influence. This internal struggle could be a major part of the fanfiction.
In the long run, Percy might grow from the experience. He could become more cautious in his relationships and less trusting. Or, if there's a chance for redemption in the fanfic, he might be open to forgiving Annabeth if she shows true remorse and has a valid reason for her actions. But initially, it would be a very difficult and emotional time for him.
Some fans might be really shocked. They are used to seeing Artemis as a more or less benevolent figure, so this sudden betrayal would be a big twist. They'd probably be eager to read more to find out the reasons behind it.
At first, Naruto would likely be extremely shocked. He has always considered Sakura a friend and teammate, so this would be a huge blow. He might question his own judgment in trusting her.
Issei would probably first try to understand why Rias has betrayed him. If he finds out that she was forced or manipulated, he might try to save her. But if it was a conscious choice, he could become angry and vow revenge. He has a strong will, and this betrayal could fuel his determination to become stronger on his own.
Percy would likely be both angry and calculating. He'd be angry because he's been kidnapped, but he'd also start thinking about how he can use his powers and skills to get out of the situation. He might try to reason with Khione if he thinks it could buy him some time to plan an escape. He'd also be looking for any weaknesses in Khione's defenses or in her personality that he could exploit.
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.
Poseidon might be extremely angry. He could immediately seek revenge on the abuser. After all, Percy is his son and he has the power to protect him.
One popular 'Poseidon betrays Percy' fanfiction might involve Poseidon being forced to betray Percy due to some ancient godly law or threat from another powerful deity. In such stories, Percy often has to face the heartbreak of his father's betrayal while also trying to figure out a way to resolve the situation and still prove his worth.
She would likely become angry. Natasha is a strong character, and being betrayed would stir up her fury. She might start planning her revenge, using her skills and intelligence to get back at Percy. Maybe she'll try to expose his true motives to others in their world or group.
Then, she would probably be angry. Annabeth is a strong - willed character. She would feel betrayed and used, and her anger would fuel her to find out the truth. She might start her own investigation to figure out what's really going on with Percy, whether he's been influenced by someone or if there's another reason for his actions.