It could also be someone new, a character created specifically for the fanfic. Maybe a new hero who has come to their world and Annabeth has fallen in love with him. This would add an element of novelty and new relationships to explore in the story.
Another possibility is that it could be a character from her past that she re - connects with. For example, an old friend or acquaintance who she had some unresolved feelings for. This could lead to a story full of twists and turns as she deals with her past and present relationships while being pregnant.
Most likely, Percy could be the father. They have a strong relationship in the original series, so it would be a natural choice. Their chemistry and shared adventures could be the basis for a story where they start a family together.
There's a chance it could be a new character introduced in the fanfiction. Maybe someone who has a mysterious past and enters Annabeth's life briefly but leaves a big impact, resulting in her pregnancy.
It could also be a new character introduced in the fanfiction. Maybe a powerful demigod from another camp who Annabeth meets during a diplomatic mission. This would create a whole new set of drama and conflict, as Annabeth would have to deal with her feelings for Percy and this new person, as well as the implications of having a child with someone other than Percy.
The fanfic could also take a more complex turn. Annabeth gets pregnant at a time when there are threats to the world. She has to deal with the fact that she's bringing a new life into a potentially dangerous situation. There could be a prophecy related to her unborn child, which adds more drama. Her pregnancy might also be a sign of hope for the future of their world, as the child could be a great hero in the making.
Another possibility is that it could be a god in disguise. Given the complex relationships between demigods and gods in the Percy Jackson universe, a god could have fallen in love with Annabeth and fathered her child. This would bring all sorts of divine drama and complications to the fanfic.
In such a fanfic, one possible consequence could be a major upheaval in the world of the story. The child would be of divine and demigod lineage, which might attract all kinds of unwanted attention from other gods and mythical beings. It could also lead to a power struggle as different factions might try to use the child for their own purposes.
In the 'Annabeth gets pregnant in high school fanfic', there could be a lot of social consequences. At school, she might face bullying or judgment from other students. Teachers might also get involved, either in a positive way by trying to offer support or in a negative way by being overly critical. Financially, it would be a big challenge as a high school student is not usually prepared to support a child.
Or, in a more creative take, it could be a new character introduced just for this fanfic. This new character could bring a whole new set of dynamics and storylines, like a mysterious stranger who has some special connection to Clary.
It could be her long - time love interest. In many fanfics, the most obvious choice would be the character she has the strongest romantic connection with in the original series.
The other gods would have mixed reactions. Some might be amused or see it as an opportunity to gain an advantage. For example, Hera, Zeus's wife, would be extremely angry and might seek revenge on Annabeth. The other demigods would be divided. Some might pity Annabeth, while others might see her as having overstepped or being too ambitious. The child, if it was born, would be a source of both hope and fear for different characters. It could be seen as a powerful ally or a dangerous threat depending on who you ask.
It could also be someone new, a character created specifically for the fanfiction. Maybe a powerful new demigod who catches Annabeth's eye, and their relationship leads to the pregnancy.