Perhaps Percy was kicked out because of a prophecy that the camp elders misinterpreted. They thought that Percy's presence would bring great danger to the camp, so they made the hasty decision to expel him. It could also be that there was some sort of political intrigue within the camp. Some powerful figures at the camp might have seen Percy as a threat to their power and influence, and so they fabricated reasons to get him kicked out.
He might be really angry at first. He's given so much to the camp, and being kicked out like that without a proper explanation would make him furious. He could storm off, vowing to find out the truth and clear his name.
One reason could be if he was wrongly accused of stealing something important from the camp. Maybe a powerful magical item goes missing and Percy is the prime suspect because of his past issues with authority. Another reason might be if he accidentally endangers the camp in some way during a mission or training exercise. For example, if he unknowingly leads some dangerous monsters back to the camp.
Perhaps she was kicked out due to personal conflicts within the pack. If there were other members who didn't like her or were jealous of her for some reason, they might have spread false rumors or convinced the pack leaders to expel her. It could also be that she was in a relationship that the pack disapproved of, and as a result, they decided to kick her out.
One reason could be causing disruption. If the 'crusade' involved making a lot of noise, blocking hallways, or disturbing classes, the school would likely take action.
One possible reason could be that she has different beliefs or values from her family. For example, if her family follows a very traditional path and she wants to pursue something more modern or unorthodox like a career in a non - traditional field that the family doesn't approve of.
One possible reason could be his unruly behavior. Naruto is known to be a bit of a troublemaker in the series, always pulling pranks. In fanfiction, this might be exaggerated, and the orphanage might not be able to handle it anymore. Another reason could be that he's suspected of being involved in something dangerous or illegal, even if he's innocent. For example, if there are strange incidents around the orphanage and Naruto is the easy target to blame because of his reputation.
One possible reason could be his prankster nature. Maybe he played one too many harmless but annoying pranks on the staff or other orphans, and they decided they'd had enough. Another reason might be the fear of the Nine - Tails within him. Even if the people in the orphanage didn't fully understand what it was, they could sense something dangerous about Naruto and wanted to distance themselves from him for safety reasons.
A plot could be that Percy accidentally breaks an ancient and sacred rule of the camp while trying to save a fellow camper. As a result, he's kicked out. He then decides to seek refuge with his mortal family, but soon realizes that monsters are targeting them too because of his connection. So he has to protect his family while also finding a way to get back into the good graces of the camp.
Maybe he's falsely accused of stealing important Gryffindor artifacts. For instance, if the Sword of Gryffindor goes missing and Harry is wrongly blamed, the house might decide to kick him out. It could be part of a plot by a jealous student or an outside force trying to disrupt Hogwarts.
Maybe he got into too many fights. Natsu has a short temper and if there were other students in the academy who provoked him or if he was standing up for someone, he might have engaged in brawls that the academy doesn't tolerate. In a place like Fairy Tail Academy, they might have strict rules about student behavior regarding fighting.