One possible story could be that Percy learned to be extremely self - reliant. He might have made friends with stray animals on the streets, like a dog or a cat that became his constant companion. He would have to find food and shelter on his own, perhaps by doing odd jobs for kind - hearted shopkeepers.
In this fanfiction, Percy might also have to deal with his own sanity. Growing up in Tartarus, the constant threat and the dark, desolate place could be a huge mental strain. He could struggle with nightmares and hallucinations, and part of the plot could be about him overcoming these mental challenges while trying to find a way back to the world above.
One possible storyline could be that Harry grows up in isolation in the cupboard under the stairs, with no real interaction with other wizards or even muggles his age. He might develop his magic skills in secret, and when he finally enters the wizarding world, he has a very different perspective compared to the original story.
His magical abilities might develop in a different way. Without the formal training at Hogwarts from an early age, he could discover his own unique ways of using magic. Maybe he would combine his street - learned skills with magic, like using his knowledge of pickpocketing to quickly snatch a wand from an enemy. His magic would be more rough - around - the - edges but also more adaptable.
There might be a monstrous creature that Percy befriends instead of fighting. This creature could have unique abilities that help Percy survive, like being able to sense danger from afar.
A group of bandits might be the main antagonists. They see Percy as someone they can easily rob or enslave since he is all alone. Percy would then have to use his skills to outwit them.
Well, one possibility is that Percy has to learn to fend for himself in a harsh world. Maybe he discovers unique powers within himself as he faces various challenges alone. For example, he could learn to hunt and build shelters all by himself, much like a survival story.
Well, for this type of fanfiction, the plot might start with Percy being separated from his usual allies very early on. He'd be forced to navigate the mortal world by himself. Since he's growing up alone, he may not have the same understanding of his Greek heritage as he does in the original series. This could lead to him making different choices when it comes to using his powers. For example, instead of using them to protect Camp Half - Blood, he might use them to simply survive in a world that seems to be constantly against him.