One possible source is the dark magic or ancient spells that exist in Tartarus. Percy might stumble upon a spellbook or be taught by a long - forgotten spirit in Tartarus. Another source could be the unique minerals or substances found in Tartarus. If he consumes or uses them in some way, they could enhance his abilities. For example, there could be a crystal that amplifies his water - based powers.
The power gain for Percy in Tartarus in fanfiction could come from his connection to the underworld deities. He might make a deal with them or earn their favor in some way. For example, if he helps Hades with a problem in Tartarus, Hades could reward him with enhanced powers. Additionally, Percy's own inner strength and his ability to endure the horrors of Tartarus could be a source. As he battles his own fears and insecurities in that dark place, he could emerge with newfound power.
In some fanfictions, Percy might gain power in Tartarus through facing and overcoming numerous deadly challenges. For example, by defeating powerful monsters that inhabit Tartarus, he could absorb some of their essence or gain knowledge from them which then transforms into power. Another way could be through making pacts with certain entities in Tartarus in exchange for power, although this would likely come with a price.
Percy could gain power by defeating the most powerful beings in Tartarus. By taking down the toughest Titans or ancient monsters that lurk there, he could absorb their power or gain respect from the other inhabitants, which would help him rule.
Maybe it's part of a plot to have Percy gain some sort of power or knowledge. In many fictional stories, a character has to go through great pain and suffering before emerging stronger or wiser. The torture in Tartarus could be a way to set up this transformation for Percy.
Perhaps he could make an alliance with some of the less hostile creatures in Tartarus. There might be beings who are also tired of the chaos and want to help Percy in exchange for something, like a promise to free them from Tartarus if he ever gets the chance. Percy is known for his charisma and ability to make friends, even in the most unlikely situations.
One possible storyline could be that Percy is tricked into betraying Tartarus by some dark force. Maybe they use his friends as hostages or manipulate his mind. Another could be that Percy believes he's doing the right thing in betraying Tartarus, but later realizes it was a huge mistake and has to face the consequences. For example, he might face the wrath of Tartarus' minions or lose the trust of his allies.
There are several possible reasons. Firstly, for the sake of drama. It makes for a very intense and emotional story when a beloved character like Percy dies. Secondly, it could be to explore the after - effects on the other characters. How would Annabeth cope? How would the Camp Half - Blood react? Also, it might be a way to show the unforgiving nature of Tartarus.
One possible scenario could be that Percy is overpowered by the various monsters in Tartarus. Maybe the sheer number of foes like the giants or the more terrifying creatures there are too much for him to handle, leading to his death.
One possible consequence could be that he becomes even more powerful in a dark way. Tartarus is full of dangerous and ancient forces. Staying there might expose him to unique and powerful magics that change him. For example, he could gain new combat skills or the ability to control certain Tartarus - born entities.
One possible plotline could be Percy's struggle for survival in Tartarus. He might have to face off against various terrifying monsters. Another could be his journey to find a way out while dealing with the psychological trauma of being in such a hellish place. And perhaps he discovers some long - hidden secrets about Tartarus itself during his time there.
Another way could be via some sort of magical artifact. For example, he discovers an ancient amulet that has the power to enhance his natural abilities. When he touches it, it starts to merge with his essence, gradually making him stronger and endowing him with new powers like the ability to control different elements related to water, not just manipulate it.