Percy might start to have nightmares about Jason's death. In the fanfiction, he could be constantly haunted by the image of Jason's last moments. During the day, he'd seem distracted, and his friends would notice that he's not his usual self. He might also start to collect things that remind him of Jason, like a small trinket Jason once gave him, and hold onto it tightly whenever he feels the pain of loss.
Percy might isolate himself. He'd find a quiet place, like by the sea, and just sit there, lost in his thoughts about Jason. The ocean, which is usually a source of comfort for him, might not be able to ease his pain this time.
Percy might be devastated. He could feel a deep sense of loss as Jason was a comrade. He might blame himself for not being able to prevent it, even if it wasn't really his fault. Percy has a strong sense of loyalty and friendship, and Jason's death would shatter his world in the fanfiction.
Well, it could vary greatly. Maybe he'd be amused. In many fanfictions, Percy has some wild adventures and Jason might find the creative interpretations of Percy's character quite funny. He could also be a bit jealous if the fanfiction portrays Percy in an overly heroic light compared to himself.
Percy often outsmarts his opponents. In the fanfiction, he might use his knowledge of his powers and the environment to his advantage against Jason. He could lead Jason into a situation where his wind powers are less effective, like in a closed - in space filled with water. Then, Percy could easily use his water powers to subdue Jason.
After Percy's death, the story could focus on Jason's guilt. Since Percy died saving him, Jason might feel responsible and try to take on more dangerous quests to make up for it. Annabeth could go on a journey to find a way to bring Percy back, which could lead to new adventures and discoveries. The demigods might also face a new threat that they struggle to deal with without Percy's skills. They would have to learn to rely on each other in new ways and develop new strategies.
He might be shocked and a bit disturbed. Percy is a heroic character, and seeing a 'dark' version of himself in fanfiction would be quite jarring. It's like looking into a distorted mirror of his identity.
If Percy is a confident character, he may take the pairing fanfiction in stride and even joke about it. For example, if he's the type who doesn't take himself too seriously, he might laugh it off and think it's a fun creative idea.
At first, it might be rocky. Percy is more of a laid - back hero, Nico is the quiet and often misunderstood one, and Jason is the dutiful leader type. But as they spend more time together, they start to see the good in each other. Percy might teach them how to have fun and not take everything so seriously. Nico could show them the power of the underworld and its secrets. And Jason would bring a sense of discipline and strategy to their group.
The author can show Jason's jealousy through his actions. For instance, when Percy is praised for a successful mission, Jason might clench his fists or look away with a scowl. He could also be short - tempered with Percy in group discussions, interrupting him or making snide remarks.
At the same time, Percy could be determined to find out why they betrayed him. He wouldn't just accept it passively. He'd be on a mission to uncover the truth, whether it was some outside influence or a misunderstanding that led to their actions. And he might also be a bit vengeful, thinking about getting back at them in some way, though his good nature might prevent him from going too far.
Ruby might show her disappointment by pouting. She's a positive character, but when faced with something wrong in fanfiction, like a wrong interpretation of her love for Crescent Rose, she'd be visibly sad.