Well, in this fanfiction, it could be that the child is a key to something in Tartarus. Percy finds the child and then realizes that he has to keep the child alive because there are forces in Tartarus that want to use the child for their own evil purposes. He might team up with some old friends or make new allies within Tartarus to safeguard the child.
The plot might involve Percy having to protect the child from the various horrors of Tartarus. Maybe he has to fight off monsters while trying to find a way to get the child out safely.
One possible plot could be that Percy stumbles upon a lost or abandoned child while navigating the dangerous Tartarus. He then has to protect the child from the various threats in Tartarus, like monsters and the harsh environment. Maybe he forms an unexpected bond with the child as they struggle to survive and find a way out together.
The child could be a prophesied one. In the world of Percy Jackson, prophecies are common. So, this child could be the one foretold in some ancient prophecy that is linked to Tartarus. Percy finding the child sets off a chain of events that will either save or doom the world. Maybe the child is the key to closing a portal in Tartarus that is releasing evil into the mortal world, and Percy is the only one who can help the child fulfill this great task.
The child could be a young demigod who got lost on a quest and ended up in Tartarus. Maybe they were trying to prove themselves and got in over their head.
One possible plot could be Percy and Zoe facing numerous dangerous monsters in Tartarus. They might have to rely on each other's unique abilities. For example, Percy's control over water could help them cross certain deadly rivers while Zoe's hunting skills could be used to fend off the approaching beasts.
One possibility could be Percy's struggle to survive the harsh conditions. He might have to find new ways to use his powers in Tartarus. For example, the strange and dark magic there could either enhance or limit his abilities. He could also form alliances with unexpected creatures. Maybe he teams up with some of the ancient and terrifying monsters that live there, but they have a common enemy, so they work together for a time.
Well, one possibility could be Percy facing his inner demons. In Tartarus alone, he might have to deal with the memories of his past failures and the fear that comes with being in such a desolate place. He could encounter strange and terrifying creatures that test his combat skills and his will to survive.
Perhaps Percy has to go to Tartarus alone because he believes it's the only way to save his friends. In Tartarus, he might encounter old foes who are now even more powerful. He has to rely on his wits and his skills with his sword, Riptide. He could also make unexpected alliances with some of the creatures there in order to survive and achieve his goal.
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.
Well, one possibility is that Percy has to deal with the various monstrous creatures in Tartarus. He might form alliances with some of the less evil ones to maintain order. Maybe he uses his powers over water in unique ways in the dark and chaotic environment of Tartarus.
Well, it could involve Percy coming back with new powers. Maybe he's more in tune with the underworld's magic. He might have made some sort of deal in Tartarus and now has to deal with the consequences in the mortal world.