One scenario could be that there are some dark forces in the fictional multiverse that consider Harry Potter fanfiction a threat to the 'original order'. Percy Jackson, being a hero, steps in. He might have to fight off some shadowy creatures that are sent to burn or erase all the fanfiction. His demigod skills like superhuman strength and his ability to control water would be very useful in this fight. And his loyalty to the idea of creativity and different interpretations (represented by fanfiction) drives him to protect it.
Maybe there is a wizard or a group of wizards in the Harry Potter universe who dislike fanfiction as they think it distorts the 'true' magic. They try to use spells to make all the fanfiction disappear. Percy Jackson, who has a sense of justice, hears about this. He uses his speed and his power over water to reach the source of these spells and stop them. He could also call on his friends from Camp Half - Blood to help him in this protection mission, because he believes that fanfiction is a form of art and should be protected.
One scenario could be during a training session at Camp Half - Blood. Maybe he's sparring with a new camper who has an unexpected fighting style and accidentally lands a hard blow on Percy. Another is when he's exploring an old, cursed temple. There could be traps that harm him, like poisoned darts that hit his leg. Or he could be in a fight with a mythical creature that has a special power to cause internal damage, like a basilisk's stare which might make his eyes and head hurt terribly.
Perhaps in a scenario where Percy is about to sacrifice himself for the greater good. Triton, seeing Percy's selfless act, is so moved that he cries. Another situation could be when Percy is being wrongly accused and is facing great danger, and Triton, who knows Percy's true nature, cries out of frustration and worry for him.
One scenario could be that Percy has some sort of magic spell cast on him that makes him smaller. Maybe a mischievous god or a powerful enemy uses a spell to shrink him for their own amusement or to gain an advantage in a battle. This would lead to some interesting situations where Annabeth has to protect him in a different way than usual.
It's highly unlikely in the context of the established stories. Harry Potter exists in the wizarding world of J.K. Rowling and Percy Jackson in Rick Riordan's world. There's no natural way for Harry to access Percy Jackson fanfiction. But if we were to break the rules and create a fan - created crossover idea, we could say that maybe a magical accident transports some Percy Jackson fanfiction into Harry's hands, but that's really stretching the imagination.
Well, one possibility could be Itachi as a wizard in the Harry Potter world. Maybe he'd be in Slytherin due to his cunning nature. He could use his Sharingan abilities in a magical way, like seeing through invisibility cloaks or detecting hidden spells.
Well, perhaps in the fanfiction, Harry could be protecting Hogsmeade from a group of dark wizards who are trying to steal some powerful magical artifacts hidden in the village. He might use his Patronus charm to fend them off and rally the villagers to fight back.
In some fanfictions, Harry might become a very influential Auror, traveling around the wizarding world to fight dark magic remnants. He could also be involved in reforming the Ministry of Magic, ensuring fairness and equality for all magical beings.
In the fanfiction, Harry squinting at Wormtail might also be a moment of intense focus. Harry could be trying to use his Legilimency skills (if he has developed them in the fanfic world) to read Wormtail's mind. He's squinting as he concentrates, trying to break through any mental defenses Wormtail might have. It could be a crucial moment in the story where Harry's discovery of Wormtail's thoughts could change the course of events.
In such a fanfiction, one possibility could be that Harry Potter defies Dumbledore over the use of certain dark magic items. Maybe Harry believes that Dumbledore is being too cautious and that these items could be used for good in the fight against Voldemort. For example, he might think that the Elder Wand could be harnessed in a different way than Dumbledore anticipates.
Well, one scenario could be that Harry moves out to escape the constant media attention in the wizarding world. He might find a quiet cottage in the countryside where he can practice magic in peace.