In this fanfiction, Percy might have adventures like battling mythical creatures in the Amazon rainforest. He could encounter new demigods and form alliances to face powerful foes.
Annabeth could definitely be one of his allies. She's smart and resourceful, and her knowledge of architecture and strategy would be useful no matter where in the universe they are. She could help Percy figure out the layout of strange alien cities or fortresses.
One idea for a Percy Jackson famous singer fanfiction could be that a famous singer is actually a demigod in disguise. Maybe they use their music as a form of magic or to communicate with other demigods secretly. For example, their lyrics could hold hidden messages about upcoming quests or threats to the demigod community.
His unexpected ally could be a minor god from the past. Maybe a god that was forgotten in his own time but still has some power in the past time period Percy travels to. This god could help Percy because they see an opportunity to regain some status through Percy's actions in the present time. Another possibility is an enemy from his own time who has different motives in the past and ends up working with Percy.
In a fanfiction where Percy Jackson travels to the past, he might try to prevent some of the tragedies that occurred in the past. For example, he could attempt to stop the first Titan War from starting. He might use his skills and knowledge from the present to change the course of history, but this could also have unforeseen consequences, like disrupting the timeline and creating alternate universes.
He might encounter advanced technology that he has no idea how to use. For example, flying cars or holographic communication devices. It would be really funny to see him struggle with these new things at first.
In this fanfiction, Percy might encounter alien species with unique powers. For example, he could meet a race that can control time, which would lead to some really exciting adventures as he tries to navigate through their time - warped worlds while also dealing with his own demigod powers.
He could meet his parents when they were young. Maybe he'd get to see his mother before she met his father and understand more about her life back then.
Well, it could be a really interesting and terrifying addition. Maybe it could be some kind of ancient monster that was locked away long ago in the world of Percy Jackson. It could be released by some dark magic or an evil demigod. The xenomorph's ability to adapt and its deadly nature would make it a formidable foe for Percy and his friends.