A more complex plot could involve a prophecy that involves a werewolf - Percy or Thalia. The two of them have to figure out what the prophecy means and how to fulfill it. Along the way, they discover a secret about werewolves that could change the entire world of the demigods. This could involve a lot of mystery, adventure, and some tense moments as they race against time to figure out everything and complete the prophecy.
Maybe Thalia is turned into a werewolf instead. Percy then has to protect her from those who want to hunt werewolves. They could end up in a werewolf pack where Thalia has to learn the ways of the pack, and Percy has to earn the trust of the pack to stay with her. This could lead to a lot of internal conflict within the pack as well as between Percy and some of the pack members.
One idea could be a pre - series fanfic where Luke, Thalia and Percy's parents all interact. Maybe they are on a quest together before the whole 'Big Three' pact drama. Another could be a fanfic where Luke and Thalia have to rescue Percy from a new and powerful monster that even he can't handle on his own. It could also be interesting to see a fanfic where they all time - travel back to an important moment in the history of the gods and have to change something to save the future.
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 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.
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 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.