Perhaps she has a connection to an important Greek god that she doesn't know about at first. When she arrives at Camp Half - Blood, strange things start to happen that draw the attention of the camp director. As she tries to figure out her place in the camp, she also has to deal with her own insecurities. She might fall in love with another demigod, which adds a romantic subplot to the story. And in the end, she might become a hero in the camp, saving it from a great threat.
Obviously, the new girl would be a main character. She could be someone with an unknown parentage at first, like many demigods. Another main character could be the camp director, who would be guiding her and trying to keep her safe. There might also be a friendly camper, like a son or daughter of Hermes, who takes the new girl under their wing and shows her around the camp.
One possible plot could be that Gabe stumbles upon Camp Half - Blood by accident. He might initially be scared but then try to take advantage of the situation. The demigods at the camp would be suspicious of him and his motives. They could try to keep him away from any secrets or magic items in the camp.
One interesting plot could be Harry Potter arriving at Camp Half - Blood and being mistaken for a demigod at first. He then has to prove his own magical abilities which are different from the demigods'. As he stays, he starts to learn about the Greek gods and their ways, and he tries to find a way to combine his Hogwarts magic with the powers and knowledge at the camp. Maybe he could even help the demigods in a battle using his unique spells.
Maybe a story where the demigods have to face a new type of monster that is immune to their usual weapons and they have to find a creative way to defeat it. For example, they might have to use the environment in a way they never have before, like using the magic of the forest around Camp Half - Blood to their advantage. This would involve a lot of exploration and discovery within the camp's boundaries and its surrounding areas.
Well, he might start showing off his ninja skills during the camp's training sessions. Maybe he'd befriend some of the demigods there easily because of his friendly nature.
A really cool plot could involve a prophecy that predicts the joining of the two camps. This could lead to some initial mistrust and rivalry among the demigods, but as they face common enemies and challenges, they start to bond and learn from each other. For example, the Camp Jupiter demigods could teach the Camp Half - Blood ones about Roman battle strategies, while the Camp Half - Blood demigods could show their counterparts some of their more unorthodox Greek magic.
One idea could be a quest that requires demigods from both camps to work together. Maybe they have to retrieve a powerful artifact that's being guarded by an ancient monster. The demigods from Camp Half - Blood could use their unique skills like Percy's water - based powers, and those from Camp Jupiter could contribute their Roman - style combat and discipline.
In such a fanfiction, Harry could discover the world of Greek mythology. Maybe he'd meet demigods and learn about their powers. He might also compare his magic from the wizarding world with the powers of the demigods at Camp Half - Blood.
Well, he could use his super speed to get around the camp really fast. Maybe he accidentally scares some of the demigods at first. He might also find that his powers work differently in the magical environment of Camp Half - Blood.
He might leave because of a personal conflict. Perhaps he has a falling - out with some of the other campers or with the camp leaders. Like if he disagrees with a new rule or policy that the camp has implemented which he thinks is unjust.