One idea could be Percy and Thalia teaming up to protect a group of young demigods who are being hunted by a new and powerful monster. They could use their combined skills, Percy's water powers and Thalia's electric ones, to fend off the attacks.
Perhaps they become guardians of a magical artifact that has the power to either save or destroy the world of the demigods. They have to face off against other demigods who want to use the artifact for their own dark purposes. Along the way, they might also deal with their own personal issues and past traumas that resurface.
Another plot could be that they are made the guardians of a secret place in the demigod world, like a hidden grove that is the source of all the magic in the land. Enemies from different camps try to infiltrate this place, and Percy and Thalia must stop them while also learning more about the true nature of the grove and its connection to their own powers.
A plot could revolve around them having to protect a young demigod who is being hunted by a powerful enemy. Percy and Thalia have different approaches to protection, and they might argue at first. But as they face more danger, they realize that they need to work together. Their sibling relationship would grow stronger as they defend the young demigod.
One idea could be that they discover a long - lost family heirloom together. They go on a quest to figure out its significance and along the way, they face various monsters and challenges. It could strengthen their bond as siblings.
Perhaps a fanfiction where Percy and Thalia are transported to an alternate dimension. In this new world, they have to figure out how to get back while also dealing with different versions of their friends and enemies. Thalia might have to face an alternate version of herself who has turned evil, and Percy could be the one to help her see the light again. It would be full of action, drama, and self - discovery.
One idea could be that Thalia and Percy are on a dangerous quest together. In the middle of it, they find a mysterious lemon - themed garden that has magical properties. The lemon trees might have fruits that can heal wounds or give them special powers. They have to protect this garden from monsters while also exploring their feelings for each other.
Maybe they are all transported to an alternate dimension where the rules of their world are different. Percy has to figure out how to use his powers without water, Thalia discovers new aspects of her lightning, and Nico has to deal with different types of underworld creatures. They must find a way to get back home while also helping the people in this new dimension.
One idea could be that they discover their twin bond gives them unique powers. For example, they can combine their skills in combat, like Percy's water control and Thalia's lightning, to defeat a powerful enemy. Another plot could involve them exploring their family history together, finding out secrets about their parents that change their view of themselves. Maybe they meet a relative who knew about their twin relationship all along but was sworn to secrecy.
The fanfiction could revolve around the relationship between Percy and Thalia as they work to safeguard Percy's guardian. It could show how their friendship or partnership develops during the course of their adventure. For example, they could start off not getting along so well, but as they face challenges, they learn to trust and rely on each other more.
One plot idea could be Percy and Thalia going on a quest together to find a lost artifact that has the power to save their camp from a new threat. Another could be them getting into an argument over how to handle a new demigod at camp, which tests their friendship but ultimately makes it stronger. Maybe they could also travel to a different realm together where they have to rely on each other completely to survive and get back home.
Maybe a plot where Dark Percy has some sort of power that Thalia needs to save someone she loves. Thalia has to convince Percy to use his powers for good in this case, and in the process, they develop a complex relationship. Percy is conflicted between his dark side and the pull he feels towards Thalia's cause.
One idea could be that in the alternate universe (au), Thalia never becomes a tree. Instead, she and Percy go on a quest together to find a powerful artifact that can stop an ancient evil from awakening. They face many challenges along the way, like battling mythical creatures that are stronger than usual due to the dark magic seeping into the world.