Perhaps Percy's cancer is caused by some dark magic or a curse from an enemy. This would lead him on a journey to not only find a cure for the physical illness but also to break the curse. He could encounter new and dangerous foes along the way, all while dealing with the symptoms and limitations of his cancer. His demigod status would add an extra layer of complexity as he tries to balance his normal demigod duties with his fight against cancer.
One possible plotline could be Percy struggling to keep his cancer a secret from his demigod friends while still trying to go on quests. He might worry that his weakened state due to cancer will let them down. Another could be Percy using his demigod powers in a unique way to fight the cancer, like trying to find a magical cure in the realms he can access. Maybe he discovers some ancient herb or potion that has the potential to heal him, but he has to face many challenges to obtain it.
One plotline could be the overprotective brother constantly trying to keep Percy out of dangerous quests. He might try to interfere with Chiron's plans for Percy, thinking he's too young or inexperienced. Another could be the brother getting into arguments with Percy's friends like Annabeth when he feels they're leading Percy into harm's way. And there could also be a plot where the brother himself gets involved in a quest to protect Percy and discovers his own hidden powers along the way.
One plotline could be Percy having flashbacks during a normal day at Camp Half - Blood. For example, while training new demigods, he suddenly remembers a particularly harrowing battle from the past. This could lead to him accidentally losing control of his powers a bit, scaring the newbies. Another could be Annabeth having nightmares about the time she was trapped in Tartarus. In the fanfiction, she might start avoiding places or activities that remind her of it, like going underground or exploring dark caves. And a third plotline could be them both trying to deal with their PTSD while on a new quest, where they have to rely on each other more than ever to overcome their mental struggles.
One interesting plotline could be the Seven facing a new, more powerful enemy that is a combination of different mythological creatures. This would test their teamwork and individual powers in new ways.
One interesting plotline could be Aphrodite taking a special interest in Percy for a quest related to love and beauty. Maybe she tasks him with finding a lost artifact that has the power to enhance or destroy love. Another could be Percy falling under a love spell cast by Aphrodite, which causes chaos among his friends as he starts acting out of character. And a third one might be Aphrodite using Percy as a pawn in a love - related game among the gods, where his actions and decisions have far - reaching consequences for the relationships between the deities.
One interesting plotline could be the siblings going on a secret quest together without the knowledge of Chiron or the other campers. They might face a new and unknown monster that tests their combined skills.
In some fanfictions, a centurion discovers a long - lost prophecy that involves Percy. This could lead to a race against time as they try to figure out the meaning of the prophecy and prevent a great disaster. Maybe it involves a new Titan rising and they need Percy's unique connection to the sea gods to stop it.
Maybe in the fanfiction, Percy's player side shows up when he has to navigate the complex social hierarchies of the demigod world. He could be seen charming different groups of demigods, from the children of Athena with his quick - witted remarks to the children of Aphrodite with his newfound 'player' charisma. This could lead to all sorts of adventures and conflicts as he tries to maintain his relationships while also keeping up his player image.
Another plotline could be Percy trying to find a way to clear his name and escape the prison. Along the way, he might make some unexpected allies among the inmates or even some prison staff who are sympathetic to his cause. This could lead to an epic adventure within the prison walls as he tries to gather evidence and outwit his captors.
One interesting plotline could be Percy trying to find a way to return home while facing new and unexpected challenges in his exile. He might encounter strange creatures or make new allies.
One interesting plotline could be a yandere character becoming overly possessive of Percy. For example, they might try to isolate him from his friends at Camp Half - Blood, seeing them as threats to their 'relationship' with Percy. Another could be a yandere secretly sabotaging Percy's quests out of the fear of losing him. They think that if he doesn't go on these dangerous quests, he'll be safe and stay with them.