One possible storyline could be that they discover their sibling relationship while on a quest together and have to deal with the shock and how it changes their view of each other.
Well, there are numerous potential storylines. For instance, they could start having dreams or visions that hint at their siblinghood. Then, as they start to believe it, they might face opposition from their respective camps. The Romans might not trust Percy all of a sudden, thinking he's using his new - found relation to Reyna for some devious plan. Meanwhile, the Greeks could be suspicious of Reyna. They could also find out that they have a special family power or legacy that only they can unlock as siblings. This could lead to a whole adventure where they search for the means to activate this power, all while dealing with the normal demigod problems like monster attacks and prophecies.
In fanfiction, the idea of Percy Jackson and Reyna being siblings is a concept that some writers like to play with. It can add an interesting twist to the story. Maybe they create a backstory where they are siblings separated at birth or something similar. But remember, this is just in the realm of fan - created stories and not part of the original mythology or the main series. Fanfiction gives fans the chance to explore relationships in new and unexpected ways.
One possibility is that they could share a divine parent in fanfiction. Maybe there's a god or goddess who is their father or mother, which would explain their connection. For example, if they had Poseidon as a father, it would be an interesting twist on Percy's story and how Reyna fits into the world of demigods related to the sea god.
One possible storyline could be Percy leading a Titan rebellion against the Olympians. Since he has a connection to the Olympian side as well, it would create a very interesting internal conflict for him.
One possible storyline could be Percy forming a band with his demigod friends. They could go on a tour across different mythical realms, performing for gods and monsters alike.
Well, if they are siblings in fanfiction, it could add a whole new layer of drama. For example, Percy might feel more protective towards Reyna, and this could change the way he approaches battles or challenges. He could be more hesitant to put her in danger, which might lead to different strategies in their adventures.
One idea could be that Percy is under a spell or some kind of mind control when he kidnaps Reyna. Maybe a new villain has emerged and is using Percy as a tool. In the fanfiction, Percy might be fighting against this internal force while Reyna is trying to figure out how to break the spell on him.
Jason is another good choice. He has a history with both Percy and Reyna. His leadership skills and his connection to the Roman side of the demigod world could bring in new plotlines. For example, he could help Percy and Reyna understand some of the more complex Roman demigod politics that they need to navigate.
A possible storyline could be that Percy is on a quest and gets lost in a different dimension which happens to be Gotham. Bruce Wayne, as Batman, finds him and initially suspects him to be a threat. But as they interact, they discover some similarities in their abilities and goals. They then start to dig deeper and find out they are related through a long - lost family connection that dates back to ancient times when the gods had some influence on the early human civilizations.
Perhaps Percy is a single dad because his partner was lost in a battle against the Titans or some other great evil. In the fanfiction, he could be dealing with the grief of that loss while still being a great father. He might take his child on adventures around the places he used to go as a teen demigod, like the Labyrinth, but this time it's to teach his child about their heritage and how to survive in a world full of mythological threats.
One possible storyline could be Percy losing hope after a major betrayal by a close friend in the demigod world. Maybe he feels like he can't trust anyone anymore and starts to isolate himself from his usual group. This could lead to a downward spiral where he even questions his own abilities and purpose.