Perhaps in this fanfic, Percy is the only survivor but he's not entirely alone. He might be haunted by the spirits of his fallen comrades who give him guidance and strength. He could use this to fight against the remnants of the evil forces that still lurk in the shadows, all while trying to rebuild the world that was shattered in the final battle.
It could involve Percy dealing with the guilt of being the sole survivor. Maybe he has to face the families of the fallen comrades and explain what happened. He might also be on a journey to find out if there was a deeper reason for him being the only one left alive.
The plot could start with Percy waking up after the battle, surrounded by the carnage. He realizes he's the only one left alive. At first, he's in shock. Then he decides to search for any other survivors, even though deep down he knows there are none. He might then go on a journey to find out why he was spared. Along the way, he meets new characters who either fear him or idolize him because of what he's been through.
He would probably become more somber. The loss of all his friends would make him less carefree. His sense of humor might still be there, but it would be tinged with sadness.
Well, if only Percy Jackson survives the final battle in the fanfic, it would be a very lonely existence for him at first. He'd be mourning all his friends and comrades. But it also means he becomes the sole bearer of all that happened in the battle. He might be seen as a hero, but also a bit of a tragic figure. All the hopes and dreams of those who died would rest on his shoulders. He'd have to figure out how to rebuild and move forward on his own, which could be a really interesting story arc.
Well, it could involve Percy going on a quest in Mars' domain. Maybe he has to retrieve some powerful weapon that was lost there. It could also include him facing off against Mars' enemies or creatures specific to that realm.
In this fanfic, Percy's identity could be in flux. Being adopted by Aphrodite, he may start to question his own self - worth outside of his heroic deeds. His new 'family' might introduce him to a more hedonistic lifestyle. He could be dragged into Aphrodite's schemes to make the world more 'beautiful' in her eyes, which could lead to him having to face off against other gods or monsters who oppose her ideas. His journey would likely be full of self - discovery as he figures out how to be Percy Jackson while also being part of Aphrodite's world.
Well, it could start with the final battle being so intense that the enemy has some sort of unbeatable advantage. Maybe a powerful new monster or a dark magic that the heroes can't counter. This leads to the deaths of all the main characters one by one. For example, Percy might go down first while trying to protect his friends, and then the others follow as they are overwhelmed.
In a Percy Jackson becomes a goddess fanfiction, the story could start with some sort of magical accident or a powerful spell that turns him into a goddess. As a goddess, Percy would have to adapt to a whole new way of life. He'd no longer be just a hero on quests but a divine being with a different set of rules. His powers would likely be enhanced, and he might gain abilities like shape - shifting or more powerful control over water. His journey would involve not only coming to terms with his new identity but also using his new powers to protect the world in a different way than he did as a demigod.
Well, it could involve Percy having some sort of special connection with the Fates. Maybe he can influence destiny in ways others can't. For example, he might be able to change the fates of his friends in dangerous situations, like when they're facing a powerful monster. This would make for an interesting dynamic as he'd have to balance the power he has with the natural order of things.
It could involve Percy facing new challenges related to the concept of balance. Maybe he has to deal with a Titan who is disrupting the natural order. For example, the Titan might be causing chaos between the mortal and the demigod worlds, and Percy has to find a way to stop it.