Well, it could be about Percy being sent to a different era in the past, like ancient Greece. He might have to deal with different versions of the gods and monsters from that time, and also find a way to get back to his own time. Maybe he teams up with some historical figures who turn out to be demigods too.
He could come back haunted by the terrors he faced in Tartarus. In the fanfiction, Percy might struggle with nightmares and flashbacks. His relationship with Annabeth could be strained as he tries to deal with his trauma alone. But then, through the help of his friends and the love of Annabeth, he slowly starts to heal. Meanwhile, an old enemy from Tartarus could be following him back to the surface world, and Percy has to gather his courage again to fight it off and protect his loved ones.
One possibility could be that Percy returns with new powers. Maybe he has some connection to the Underworld now that he's come back from the dead. He might be able to control the dead or has some knowledge about the afterlife that he uses to help his friends in battles against new and more powerful enemies.
There could be ancient Greek heroes that Percy meets in the past. For instance, Heracles. Since Percy is from a different time, Heracles might not be exactly as the legends say, and they could have an interesting dynamic. Another potential character could be an oracle from an older era who has different prophecies related to Percy's situation.
Well, he might find that his demigod powers work differently. Maybe in this new world, the water doesn't respond to him in the same way as in his own world. He could also encounter new and strange creatures that he has never seen before, and have to figure out how to deal with them without the help of his usual friends from Camp Half - Blood.
Well, it could be about a Saiyan who travels through time and has to adapt to a different era. Maybe he has to face new enemies or form unexpected alliances in this new time period.
Well, perhaps in this fanfiction, Percy Jackson is sent on a time - travel mission by the gods. But he discovers that his friends or allies have betrayed him. Maybe they've made a deal with an enemy from another time period. For example, they could have promised to help Kronos in the past in exchange for power in their own time. Percy then has to not only deal with the time - travel chaos but also face the betrayal and find a way to set things right.
Maybe Percy hides because he discovers a secret about the gods that they don't want him to know. For example, he might find out about some underhanded deal among the gods that could endanger the demigods. So, in order to protect himself and his friends, he decides to hide.
A great plot could be Percy being sent on a top - secret mission by the army. This mission could be related to some ancient artifact that has military applications but also ties to his demigod world. Along the way, he meets other demigods who are also in the military for various reasons. Together, they have to overcome not only military enemies but also mythical creatures that are after the same artifact.
Well, the plot might start with Percy being sent on a special mission by the gods. They need someone with his quick reflexes and sharp eyesight to be a sniper. Along the way, he has to deal with the moral implications of taking lives from a distance. He might also face challenges in terms of getting the right equipment and training. His friends could be initially skeptical of this new role for him, but as they see him succeed in various battles, they come to accept and rely on his sniper skills.
One possible plot could be Percy using his bike to travel across the country to find and protect other demigods. He could encounter various monsters along the way and use his biker skills, like sharp turns and high - speed maneuvers, to evade them.