Well, perhaps Percy comes back to find his old friends have changed a great deal. Maybe some have new powers or positions in their world. He could be faced with a new threat that only he can help to defeat because of his unique past experiences.
Well, he might disappear because of a powerful curse from an ancient enemy. Maybe he gets trapped in a different dimension. When he returns, he could have new powers or knowledge. For example, he might have learned some secret magic from the other dimension that helps him defeat a new threat in the Percy Jackson world.
Well, he might face new monsters. For example, some ancient and more powerful versions of the ones he's already fought. Maybe there are new quests waiting for him at the camp, like finding a lost artifact that has the power to either save or destroy the camp.
Well, one possibility could be that Percy has been on some sort of adventure and during that time, he discovers a child in need. He decides to take the child under his wing and brings the child back to his world. Then, he has to deal with the reactions of his friends and family, who are both surprised and a bit worried about this new addition.
Well, it could involve Percy coming back with new powers. Maybe he's more in tune with the underworld's magic. He might have made some sort of deal in Tartarus and now has to deal with the consequences in the mortal world.
One possible plot could be that Percy returns with new powers. Maybe he was resurrected by some ancient magic or a powerful deity who has a plan for him. He then has to deal with the shock and awe of his friends and also face new enemies who are either threatened by his return or want to use his newfound powers for their own gain.
One possible plotline could be Percy having nightmares about his time in Tartarus. He might struggle with PTSD, which could affect his relationships with his friends and family at Camp Half - Blood. Another could be that he brings back some sort of dark power or knowledge from Tartarus that he has to figure out how to control or use for good. Maybe he discovers a way to close the entrance to Tartarus permanently so that no more monsters can come out and endanger the demigod world.
His old friends like Annabeth could be main characters. She might have been leading the group in Percy's absence and now has to adjust to his return. Grover could also be there, still being Percy's loyal friend and perhaps having some new knowledge about the world of magic and nature.
In addition to Annabeth and his family, he might interact with other demigods he knew before. They could be in awe of his new godlike state. There could also be some characters from the godly realm who are interested in Percy's return. They might want to use his power for their own purposes or they could be there to guide him on how to fully control his newfound abilities.
In this fanfiction, a plot twist might be that Naruto returns to Sakura, but he brings with him a secret that could endanger the whole village. Sakura is then faced with a dilemma: whether to protect Naruto or the village. Or perhaps, Naruto returns to find that Sakura has made a powerful enemy while he was gone, and now they both have to deal with this new threat together. It could also be that Naruto's return is part of a bigger plan by an unknown villain, and Sakura gradually discovers this as she interacts with Naruto.
Perhaps Naruto returns to the world with new powers or abilities he gained during his time away. He might use these to solve long - standing problems in the ninja world, like better relations between different villages. He could also teach the new generation of ninjas what he has learned.