He could be running away to pursue a lead on Voldemort or some other dark magic on his own. Harry has always been the one to take matters into his own hands. If he got a tip about a crucial piece of information related to defeating Voldemort that was outside of Hogwarts, he might run away to follow it without waiting for permission or support from the school.
Perhaps he runs away because he feels misunderstood. In the fanfiction, the other students or even some of the teachers might wrongly accuse him of something. He could be tired of constantly having to defend himself. Like if he was wrongly blamed for a serious incident at Hogwarts, and no one seemed to believe his innocence, he might just leave in frustration.
Maybe he wants to escape the constant danger in the UK wizarding world. Voldemort's followers might still be a threat even after his defeat, and France could seem like a safe haven.
One possible reason could be that he feels unsafe at Hogwarts. Maybe there are threats from dark wizards within the school that the teachers are unable to fully protect him from. Sirius, being his godfather, represents a safe haven.
In fanfic, one reason could be that he might feel constantly in danger at Hogwarts. With all the dark forces targeting him, he could think running away is the only way to keep his friends safe. For example, if Voldemort's followers keep infiltrating the school, Harry might feel responsible and decide to leave to draw the danger away from others.
Perhaps in the fanfiction, Harry Potter runs away from Britain because he is disillusioned with the way the Ministry of Magic operates. There could have been a major event where the Ministry fails him or betrays his trust. Also, he may be seeking a place where he can explore his magic without the constraints and expectations that come with being 'The Boy Who Lived' in Britain.
In some fanfictions, Harry might be expelled for being wrongly accused of using dark magic. Maybe someone framed him by planting dark magic items in his dorm. Another reason could be that he continuously breaks school rules in a way that the school can't tolerate, like sneaking into the Forbidden Forest too many times without permission.
One reason could be she feels extremely pressured by the high expectations at Hogwarts. Everyone expects her to be perfect in academics and problem - solving. Another might be that she discovers some dark secret within the school that she's afraid of, like a hidden plot by a group of dark wizards among the staff or students. Or she could be running away to protect her friends. If she believes that her presence at Hogwarts endangers Harry and Ron, she might choose to leave to keep them safe.
One reason could be that it doesn't stay true to the original lore. For example, if the fanfiction changes the fundamental rules of magic in Hogwarts that were established in the original series. Another reason might be that the characters' personalities are distorted. Harry Potter is known for his courage and self - sacrifice, and if the fanfiction turns him into a cowardly or self - centered character, it could be rejected.
One reason could be to escape the constant media attention and pressure that comes with being in the wizarding world's spotlight. Harry especially has always had the eyes of the public on him, and running away might be a way to get some peace.
One reason could be that he wants to escape the constant attention and pressure. After all he's been through, he might just want a normal life away from the wizarding world's spotlight. Maybe he moves to a far - off place where no one knows who he is.
She could run away because of a broken heart. Maybe she had a relationship that ended badly, and she needs to get away from the memories. In the process of running away, she could meet new people who help her heal and grow as a person. This type of storyline often explores the more vulnerable side of fem Tsuna.