Obviously, Nico is one of the most important characters as the story seems to center around him. And of course, the gods are important too as they are the ones watching Nico.
Well, it could be that the gods are watching Nico in Tartarus as a form of judgment. Maybe they want to see if he has truly changed or grown. They might be using his time in Tartarus as a test of his character. Nico, being in Tartarus, is likely facing numerous terrifying creatures and dangerous situations, and the gods' watching could add an extra layer of tension, like they are waiting to see if he will succumb to the darkness or rise above it.
Surviving in Tartarus would require them to adapt quickly. The place is full of unpredictable and extreme conditions. They need to find shelter from the various hazards, like the volcanic eruptions and the attacks of powerful monsters. Their friendship and mutual trust would also be a great strength. They can support each other emotionally, which is crucial in such a terrifying and desolate place. For example, when one of them is feeling down or hopeless, the other can cheer them up and keep their spirits high, so they can keep on fighting for survival.
It could be really interesting. Maybe they would gain a new perspective on Nico. They might be amused by the creative interpretations of his character in the fanfiction.
One possibility is that they encounter other lost souls in Tartarus. These could be the souls of ancient heroes or villains. Interacting with these souls could either help them or put them in more danger. For example, some souls might offer them advice on how to navigate the treacherous terrain of Tartarus, while others might try to deceive them into making wrong decisions. And they would surely be tested both physically and mentally. The harsh environment of Tartarus would push their limits, and they would have to overcome their inner fears and doubts to have any chance of escaping.
You can start your search on the major fanfiction websites. AO3 has a very inclusive search function. You can input 'gods read about Tartarus' as a phrase and see what comes up. FanFiction.net also has a search feature. If you don't find much there, consider looking at smaller, more niche fanfiction communities related to the relevant mythology. These might be on platforms like Wattpad or even in some Facebook groups dedicated to fanfiction. But always be cautious of the quality and the authenticity of the fanfictions you find.
The plot could revolve around Percy's journey of self - discovery in Tartarus. Sent there unjustly by the gods, he could start to question his past actions and his relationship with the divine. As he battles the horrors of Tartarus, he may develop new powers or skills. He could also be on a mission to expose the true nature of the gods' actions, which led to his banishment to Tartarus. Along the way, he would face challenges that test his physical and mental strength to the limit.
One common theme is power and responsibility. Since they become gods, they have to handle new - found powers while also taking care of the world. Another theme is identity. They are no longer just demigods but gods, so they have to re - define who they are.
One challenge is the jealousy of other gods. Since they are new gods, the older, more established gods might not like the attention they get or the new ideas they bring. Another challenge is controlling their powers. As mentioned before, going from demigod to god means a huge jump in power level, and it's not easy to get used to. For example, Percy might accidentally flood a city while trying to create a small puddle for fun.
Apollo, being the god of arts, might appreciate the creativity in the Nico fanfiction. He could enjoy the different ways Nico's character is developed and the stories that are spun around him.