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.
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.
Some fanfictions might focus on the relationship between the three of them. It could be a story where Percy, Luke, and Thalia are stranded in a strange place. They have to rely on each other to survive. During this time, they start to understand each other better. Percy learns more about Luke's past that made him turn bad in the first place, and Thalia tries to be the mediator between them, leading to a more complex and interesting dynamic.
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.
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.
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.
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 and Percy meet as kids before all the chaos. They could become friends briefly and that friendship could add an interesting layer to their later enmity. Another could be a fanfic where Luke is given a second chance after his fall and has to work with Percy to redeem himself. Maybe they have to go on a quest together to save someone important from a new threat in the demigod world.
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 story where Fem Percy and Luke team up against a new, powerful enemy that neither Camp Half - Blood nor Luke's former allies can handle alone. They have to put aside their differences and work together, with Fem Percy using her unique take on Percy's powers and Luke using his battle - hardened skills.
One idea could be a pre - series story where Thalia and Luke are training together in Camp Half - Blood and they stumble upon a mysterious prophecy that seems to involve them both. Another could be a story set during Luke's fall to the dark side, and Thalia tries to save him by appealing to their old friendship.