In fanfiction, Jackson might worry about his sister because she could be involved in a relationship that he thinks is not good for her. For example, she might be dating someone who has a bad reputation or is from a rival group. Another reason could be that she's lost in a strange world within the fanfiction story, and Jackson is concerned for her safety and well - being. He could also be worried if she's getting bullied or harassed in the fanfiction world.
Maybe his sister is in some kind of danger in the fanfiction, like facing a powerful enemy or being in a tricky situation. It could also be that she's ill and Jackson is worried about her health.
It could be the weight of his responsibilities. Percy has always had a lot on his plate, saving the world multiple times. The constant pressure to be the hero might finally get to him, making him feel like he can't keep up. He might start to think that one day he'll fail and cause great harm.
It could also be related to her popularity among their peers. If his sister is more well - liked and has a lot of friends, Naruto, who has often been an outcast, might feel envious. He might wish he had the same social skills or charm that his sister has, which allows her to fit in so easily.
Perhaps she's a sister who was thought to be dead but actually survived. She could have been corrupted by the experiences she had while being 'dead'. When she returns, she blames Percy for not saving her properly. This false blame leads her to betray Percy. She could start spreading rumors about Percy being a coward or a bad leader among the demigod community.
One possible reason could be to protect her. Naruto might believe that by leaving, he can draw danger away from his sister. For example, if there are powerful enemies targeting him, he doesn't want his sister to get caught in the crossfire.
One possible reason could be to protect her. Maybe she has some special power that attracts dangerous enemies, and Naruto, being the strong and protective character he is, seals her power to keep her safe from those who might misuse it.
Another possibility is that they leave because of a sense of disillusionment. They could have witnessed some corruption or unfairness within Konoha's leadership or among the ninja community. This makes them lose faith in the village and decide to start anew elsewhere.
One possible plot could be Percy feeling a deep sense of betrayal and loneliness. He might struggle with his self - worth as he wonders why his sister left him. This could lead him on a journey to find answers about his family and his own identity, perhaps even uncovering secrets about his demigod heritage that his sister knew and he didn't.
The sister could be under the control of a powerful god or goddess who has a grudge against Percy. She might be forced to betray him. For instance, she could lead Percy into a trap set by the god. She could lie to him about a mission, saying it's a rescue mission but in fact it's a trap where the god is waiting to take revenge on Percy for some past deeds. This would be a really heart - breaking betrayal for Percy as he trusts his sister.
The sister could be bullying Naruto out of envy. If Naruto has some special abilities or talents that she doesn't, she might be jealous and lash out at him.
It could be that his sister has some special abilities or talents that the family or the village values more. For example, if she has a very rare and powerful bloodline limit, everyone's attention would be drawn to her. In a ninja world, power and potential are highly regarded, so Naruto might be overlooked because his sister seems to have more of that 'special something' at first glance.