One interesting plot could be Percy's struggle to control his new powers as the God of Tartarus. He might face challenges from other gods who are threatened by his rise. Another could be his journey to reform Tartarus, making it less of a hellish place. For example, he could try to bring some order to the chaotic entities that reside there.
Perhaps a plot where Percy forms an unlikely alliance with some of the more neutral or even hostile creatures in Tartarus. He could use his charm and wits to convince them to help him in his struggle against the greater evils of that place. In this way, he learns more about the complex hierarchy and politics within Tartarus.
Some Tartarus fanfictions focus on Percy's mental state while in Tartarus. It could explore his nightmares and how he copes with the overwhelming sense of despair. For instance, he might have visions of his friends and family in danger back on the surface, and he has to find the strength within himself to keep going in the face of such mental torture.
One interesting plot could be Percy finding out that a so - called 'ally' of the gods has actually been manipulating him all along, leading to his perceived betrayal of the gods. Maybe this ally frames Percy for a crime against the gods, causing him to lose the trust of his friends and have to fight alone.
Another interesting plot might involve Percy facing off against other gods. As the God of Water, he could be seen as a threat or a potential ally. Some gods might try to undermine him, while others might seek his help. This could lead to political intrigue within the pantheon, which is always exciting in fanfiction.
One interesting plot could be Percy's struggle to survive in Tartarus alone. He might have to face the various monsters there without his usual allies. Another plot could involve him finding a way to escape Tartarus using his wits and the powers he has. Maybe he discovers some secrets about Tartarus that no one else knows.
A great plot could involve Percy finding a way to use the unique environment of Tartarus to his advantage. For example, there could be some sort of energy in Tartarus that he discovers he can harness to become stronger, but it has a dangerous side - like it might slowly corrupt him. He then has to struggle with the decision of whether to keep using it to get out or resist it.
Well, a great plotline might be Percy's struggle with his own inner demons while in Tartarus. He could be haunted by his past failures and the fear of not being able to save his friends. This internal battle could be paralleled with his physical battles against the terrors of Tartarus. Also, there could be a plotline where Percy discovers a long - lost power within himself that is the key to either ruling Tartarus or escaping it.
Well, a plotline could be Percy having to adapt to the extreme and harsh environment of Tartarus. The place is full of darkness and danger. He might have to learn to harness the strange and dark energy that exists there in order to defend himself. There could also be a plot where Percy is forced to make difficult choices. For instance, he might be presented with an option that could save him but at a great cost to others. This would test his moral compass and show how much he has grown as a character in this extreme situation.
One more plot idea could be that Percy and Annabeth are somehow affected by the dark magic of Tartarus. It changes them in some way, either physically or mentally. They then have to deal with these changes while still trying to escape. This could lead to some really intense internal and external conflicts as they struggle to stay true to themselves and also find a way out of Tartarus.
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.