A really interesting plot could be that the prophecy is misinterpreted at first. Thalia thinks it means one thing, like she has to sacrifice herself to save the world. But as she delves deeper into the mystery, she realizes that it's about a different kind of sacrifice, like giving up her new - found power or a relationship that she values, which is much more complex and heart - wrenching.
Perhaps the prophecy involves Thalia having to team up with an unexpected ally. For example, a former enemy who has also been touched by the prophecy in some way. They would have to overcome their differences and learn to trust each other while facing numerous challenges like dangerous quests and battles against powerful Titans or other mythical foes.
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 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.
One idea could be that Percy and Thalia have to go on a secret quest together, away from the rest of the demigods. During the quest, they discover new powers within themselves and also realize their feelings for each other are deeper than just friendship. Another could be a story where they are trapped in a magical realm and have to rely on each other's skills to escape, with lots of action and some tender moments in between.
One idea could be exploring how their demigod powers are affected during the pregnancy. For example, Percy's control over water might become more erratic due to hormonal changes. Another could be the reactions of their friends and the demigod community. Some might be supportive, while others might fear for the future of the half - bloods. Also, they could face challenges from the gods, as the birth of a new demigod with such powerful parents could shift the power balance in the mythological world.
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.
Thalia could be developed by showing her struggle with the weight of the prophecy. For example, she might have nightmares about it, which would make her more vulnerable and human. This would also add depth to her character as she tries to hide her fears from others while still being a strong leader.
One idea could be that Percy is chosen by a prophecy to help Artemis in a quest to retrieve a powerful, lost artifact. Maybe it's a magical weapon that was stolen by a new, unknown enemy. Percy's skills in water and combat would be crucial in navigating the dangerous terrains and battling foes on the way.
One idea could be that Percy discovers he has a long - lost connection to Thalia. Maybe in a magical twist, a prophecy reveals that he is fated to be like a father figure to her. He could then use his powers and experience to train Thalia, much like Chiron trained him.
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.