In the fanfiction, Percy might face new challenges related to his demigod status. Maybe he has to deal with the aftermath of the war, like rebuilding Camp Half - Blood or helping new demigods adjust.
One possible plot could be Percy and his friends dealing with the aftermath of the war in the mortal world. Maybe they have to hide their demigod identities even more carefully as the war has drawn some unwanted attention. They could also be working on rebuilding Camp Half - Blood and trying to make it safer for new demigods.
Perhaps some of the demigods from other camps that he didn't interact much with before could become his new allies. They might see his leadership during the war and want to be part of his group, to learn from him and fight alongside him in any future conflicts.
In fanfiction, Percy might finally get some peace. He could go back to school and try to have a normal life, but still be on guard for any new threats. Maybe he'd focus more on his relationship with Annabeth and they'd plan for their future together.
It could be a rogue demigod who was on the losing side of the Giant War and is now seeking revenge. This demigod might have found some dark power or be allied with some minor but dangerous mythical creatures.
There could be new demigods. Maybe some who were hidden during the giant war and now come out. For example, a demigod of a less - known god or goddess.
It could also change the power dynamics. Percy had unique powers and abilities that were crucial in the war. Without him, the opposing forces might gain an upper hand. For example, his control over water was a major asset in battles against the giants. His death would mean the loss of that strategic advantage.
Another option could be a new demigod. A character who was not very involved in the war but is now thrust into the post - war chaos. This new character could bring a fresh perspective and could be learning about the demigod world and its history while also trying to help in the rebuilding and healing process.
Maybe the characters start to rebuild their lives. For example, they might focus on restoring the damaged places and re - establishing relationships that were strained during the war.
It's popular because fans love Percy and Annabeth's relationship. After the giant war, there's a lot of room for exploring how they move forward. Their relationship has been through so much during the war, and seeing it develop further in fanfiction is appealing.