She might be shocked and feel a great deal of sympathy for Percy. She could immediately try to comfort him and assure him that he's safe now.
Zoe could become angry, especially if there's someone she can direct that anger towards, like the abuser. She might vow to protect Percy from any further harm and be very protective of him from that moment on. For example, she may start to keep a closer eye on him during their daily interactions in the story's setting, whether it's at school or in some fictional realm they inhabit together.
Zoe might also feel a sense of guilt, thinking that she should have noticed the signs earlier. This could lead her to overcompensate in her efforts to help Percy. She could start spending more time with him, trying to get him to open up about his experiences, and even offer practical help like getting him in touch with people who can provide professional support if such a concept exists in the fanfiction world.
She might be shocked and angry. Thalia is a protective character. She could immediately vow to find those who abused Percy and make them pay. For example, she might start by gathering information about the abuse, asking Percy for details in a gentle way to not further traumatize him.
Well, Annabeth is a strong character. When she finds out Percy was abused in the fanfiction, she likely starts by trying to comfort him. She may use her intelligence to figure out how to help him deal with the trauma. Maybe she'll also plot some sort of revenge against the abuser in her own clever way, all while being a great source of emotional support for Percy.
She might be shocked at first. Then she could become extremely protective of Percy. She would likely confront those who are responsible for the abuse and make sure Percy is safe from further harm.
Percy could become more withdrawn at first. The revelation of his abuse might make him more self - conscious and less trusting.
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.
She would probably be furious. Artemis has a strong sense of justice and protecting the vulnerable. So, she would likely immediately start to plan how to deal with those responsible for Percy's abuse.
Nico might be initially shocked. He could feel a deep sense of anger towards whoever was responsible for Percy's abuse. Then he would probably become very protective of Percy, vowing to keep him safe from any further harm.
Another reaction could be that Percy is worried about Sally getting into trouble because of him. He might try to convince her to stay out of it, fearing that the abuser or those associated with the abuser could harm Sally. But at the same time, deep down, he wants her support and protection.
She might be horrified and immediately take steps to protect Sirius. For example, she could confront the abuser or report it to the proper authorities within the wizarding world.
Well, Bellatrix is a very unpredictable character. In this fanfiction scenario, she could react with glee. Since she's on the side of the Dark Lord, she might think that Harry's abuse has made him more vulnerable. She could also be curious about who would dare to abuse 'the Boy Who Lived'. However, she might also be angry that someone else has been causing harm to Harry when she believes that's her Dark Lord's prerogative.