One possible storyline could be Percy having to deal with the constant gloom and the various creatures that lurk in the underworld. He might try to find a way to bring some light or hope to the place. For example, he could use his powers to make small areas more habitable for the lost souls there.
Perhaps Percy discovers a hidden part of the underworld that no one else knows about. This could lead to him finding secrets about the gods or even a way to change the nature of the underworld itself. He may encounter new and strange creatures that are unique to this hidden area and form alliances or face new enemies.
In a fanfiction where Percy lives in the underworld, he could be on a mission to redeem the souls of some of the most heinous criminals. This would be a huge task as the underworld is filled with souls that have committed great evils. He would have to use his wits and powers, and maybe even make some difficult bargains with the rulers of the underworld to achieve this goal.
A practical answer is Chapter 163, because it turns the idea into a concrete scene. The chapter opens with Su Yinwan entered a small room, guided by a staff member., adds pressure through Shang Shaojing slightly clenched his fists, his expression growing even..., and ends on Moreover, by doing so.
A practical answer is Chapter 135, because it turns the idea into a concrete scene. The chapter opens with The sun blazed down mercilessly, but thankfully, the path to the mountain..., adds pressure through At this moment, it seemed more likely to be grim than not., and ends on Are you healed from.
A practical answer is Chapter 132, because it turns the idea into a concrete scene. The chapter opens with The new girl in the live-streaming room went crazy., adds pressure through Stay away from my fragrant and fresh Brother Daniu!] [Not only has the..., and ends on He stir-fried the other.
A practical answer is Chapter 180, because it turns the idea into a concrete scene. The chapter opens with In the end, everyone received gifts that were completely opposite to what..., adds pressure through Jiang Yan is Jiang Li's brother;
The best chapter pointer here is Chapter 160, "The Mushroom-Picking Party of Six". It opens with As the sky gradually darkened, the originally mild drizzle began to... and closes on Then came Shu Yan and Jiang Li, while He Yun silently moved to the back of....
If you want the clearest chapter reference, go to Chapter 138. Early on, Is there such a good deal?; later, the chapter leans on Qi Tianyu quickly nodded in agreement and knelt down to start helping....
Look to Chapter 166 for the clearest answer. It begins with Only after everyone in the small courtyard had left, did Zhao Lang stride..., keeps building through Through the window, he saw the girl sitting at the table reading, her face..., and lands on However, after interviewing the villagers, no.
Chapter 159 is the strongest chapter-level answer because it starts from Seeing the red light of the camera turn on, Su Yinwan looked at the... and follows through on Shang Shaobai, who was browsing through files, received a call from his....
If you want the clearest chapter reference, go to Chapter 120. Early on, Facing the sudden and somewhat strange request from Jiang Li, Director Sun...; later, the chapter leans on But, as if by some mysterious force, he still instructed his assistant to....
If you want the clearest chapter reference, go to Chapter 120. Early on, Facing the sudden and somewhat strange request from Jiang Li, Director Sun...; later, the chapter leans on But, as if by some mysterious force, he still instructed his assistant to....