It could be due to a conflict within the Order of Phoenix or some other wizarding organization he's involved in. He might discover something that goes against his beliefs and rather than fight it from within, he chooses to run away to figure things out on his own. For example, if there are secrets being kept that he disagrees with, it could be a trigger.
Perhaps he has a love interest that the family doesn't approve of. In the wizarding world, family opinions can be very strong. If he falls in love with someone from a different or controversial background, he may run away to be with that person without the family's interference.
One possible reason could be family pressure. In the Weasley family, there are high expectations and a lot of chaos. Percy might feel suffocated and decide to run away to find his own path. Maybe he's tired of always being in the shadow of his more popular siblings and wants to prove himself on his own terms.
One reason could be his ambition clashing with his family values. Percy is often very career - driven in the original story. Maybe in the fanfiction, his pursuit of success at the Ministry of Magic leads him to make decisions that isolate him from his family, ultimately causing him to run away. For example, he might be given an important assignment that goes against the Weasley family's stance on certain magical politics.
Perhaps he was influenced by some new friends he met who had a different lifestyle or view of the world. They might have convinced him that running away from home was an exciting adventure and a way to break free from the restrictions at home.
Well, perhaps they run away because they discover some dark secrets about the wizarding world that others don't want them to know. They might fear for their lives if they stay, so they choose to flee. It could also be that they are simply seeking adventure. The daughter of Harry and Sirius might inherit their adventurous spirits, and they both decide to run away to explore the unknown parts of the wizarding world and beyond.
It would cause a great deal of sadness. Molly Weasley, being a very family - oriented mother, would be heartbroken. She might constantly worry about Percy's well - being and feel like she failed as a mother. The younger Weasley siblings would also be affected. Ron, for instance, might feel confused and a bit betrayed, as Percy has always been a role model to some extent.
One possible reason could be to escape from false accusations. In the 'Harry Potter' universe, Sirius was wrongly accused of betraying the Potters. So in the fanfiction, he might run away to avoid being captured and to find a way to prove his innocence.
One possible reason could be that she feels overwhelmed by her responsibilities. In the world of Equestria, Twilight has a lot on her plate, like studying magic, taking care of Spike, and helping her friends. In fanfiction, the writer might explore the idea that she just needs a break from it all and runs away to find some peace.
Maybe she feels left out in the family. In the Encanto story, Mirabel is the odd one out not having a special gift. This could make her feel so alone and unwanted that she decides to run away.
One possible reason could be that Naruto feels like an outcast. Despite being part of Team 7, he might think that Sasuke and Sakura are closer to each other. Naruto has always been alone before joining the team, and if he feels excluded again, it could lead to him running away. Also, he might be afraid of endangering his teammates. Naruto often attracts trouble because of the Nine - Tails inside him. He may think that by leaving, he can keep his friends safe from the enemies who are after him for the power of the Nine - Tails.
He could run away to a far - off wizarding village. There are many small, secluded villages in the wizarding world that are not well - known. For example, a place like Hogsmeade but much more remote, where he can start anew and not be bothered by his past or family.
Another plot could be that they run away because they are disillusioned with the way things are in their community. Percy and Thalia might not agree with the rules or the leadership. So they decide to run away and start their own little 'society' in the woods. They could meet other outcasts along the way and form a unique group. They would have to figure out how to govern themselves and deal with any challenges that come their way, like wild animals or other groups that don't like their presence.