Another plot could be Percy discovering a long - lost relative among the children of Hades. This relative has some sort of power or knowledge that could change Percy's understanding of his own identity and his place in the demigod world. It could lead to a journey of self - discovery for Percy as he navigates this new family connection within the dark and often misunderstood realm of Hades.
A third plot might involve Percy being sent on a quest by Hades himself. Hades could be facing a problem that only Percy, with his connection to Poseidon and his own hero - like nature, can solve. This could be something like a stolen artifact from the underworld that, if not retrieved, will cause chaos in both the underworld and the mortal world. Percy would have to work with the children of Hades, who are initially distrustful of him, to complete the quest.
A plot could revolve around the son of Hades having to face a new and powerful monster that is specifically targeting him because of his heritage. This would lead to a series of adventures where he has to use his unique powers from Hades to survive and protect his friends. For example, he might be able to control the undead in new and unexpected ways to fight this monster.
One idea could be Percy having to deal with the stigma of being associated with Hades in the demigod world. He might face distrust from other demigods who are scared of Hades' reputation.
One idea could be Percy discovering new powers related to being the son of Hades. For example, he might be able to control the shadows in a unique way that no other demigod can. He could use this power to spy on enemies or to travel quickly through the underworld.
Maybe the son of Hades in the fanfic has a special bond with a particular type of monster that is usually associated with death, like a Cerberus - like creature. Percy Jackson and his friends are initially scared of this bond but then realize it could be used to their advantage. For example, the son of Hades could use this bond to control the monster and have it help them in a battle against a common enemy. The fanfic could also explore how the son of Hades tries to fit into the world of Camp Half - Blood while being different from the other demigods.
One idea could be the self - insert character discovers they have a unique power related to Hades that no one else in the Percy Jackson world has. Maybe they can control a special type of underworld creature that hasn't been seen before. This could lead to a series of adventures where they have to prove themselves to the other demigods and also to Hades himself.
One idea could be Percy having to navigate the Underworld politics due to his relation to Hades. He might face challenges from other underworld creatures who don't trust him. Another could be Percy using his newfound powers as the son of Hades to fight against an ancient evil that threatens both the mortal and underworld realms. Or perhaps he has to deal with the stigma of being Hades' son in the demigod community and prove himself worthy.
Another plot could involve Percy's relationship with his father, Hades. Maybe Hades has some grand plan for Percy that he doesn't fully understand at first. Hades could be trying to use Percy to gain more power in the world of the gods, but Percy resists and has to fight against his father's wishes while also dealing with the internal conflict of not wanting to completely turn his back on his family.
You could write a fanfiction where the House of Hades has a sort of time - warp effect. The demigods find themselves reliving parts of their past traumas while in there. This would not only be a great way to explore their backstories more but also add an element of psychological horror. Also, what if there was a character from Greek mythology that they thought was long dead but is actually alive and trapped in the House of Hades? They could then try to rescue this character while also fulfilling their main mission.
One idea could be exploring the backstories of the minor characters in the House of Hades more deeply. For example, the story could focus on how a particular spirit in the House got there and what their life was like before. Another plot idea could be a time - travel twist where Percy and his friends are sent back to an important moment in the history of the House of Hades to change something that has a big impact on their present situation. A third idea might be a 'what - if' scenario, like what if Percy had to face a challenge alone in the House of Hades without his friends and how he would overcome it.
One idea could be that the daughter of Hades has the power to communicate with the dead in a unique way, like seeing their memories. She could use this to help Percy solve a mystery that involves an ancient curse. Another plot could be her struggle to fit in among the other demigods because of her dark powers and the stigma associated with Hades. Maybe she discovers a hidden power within herself that is related to her father's realm and has to learn to control it while also dealing with the outside world's view of her.