Well, a cool plot twist might be that the fem Percy Jackson raised by Hestia has a special connection to the underworld. Since Hestia is the goddess of the hearth, and the hearth is a symbol of life and warmth, her influence on Percy could make Percy a sort of bridge between the living world and the underworld. Maybe she can communicate with the dead in a unique way that no other demigod can. Also, it could be that Percy discovers she has an unknown parentage related to an underworld deity, which throws her whole identity into chaos. This would change her journey in the fanfic completely as she tries to figure out who she really is while still being raised by Hestia.
One idea could be Percy having a vision or encounter with Hestia that leads him to a hidden part of the Underworld where the warmth of Hestia's hearth is the only thing keeping a powerful and dangerous entity at bay. He has to work with Hestia to keep it that way.
The fem Percy in this fanfic would likely be more nurturing. Since she was raised by Hestia, the goddess of the hearth and home, she'd have a stronger sense of family and community. In contrast to the original Percy who was more impulsive in combat, fem Percy might be more strategic, thinking about how her actions affect those around her. Also, her relationship with her powers would be different. She might see her water powers as a way to cleanse and heal rather than just for fighting.
One interesting plot twist could be that Percy discovers a new power within the gamer - like world that he didn't know he had. Maybe he can suddenly control the elements in ways he couldn't before, like creating ice sculptures out of thin air when his main power was water - based before.
One interesting 'Percy Jackson Raised Himself' fanfic could be where Percy has to rely solely on his own wits and limited knowledge of his demigod powers at a very young age. He might create his own unique training methods and form alliances with unexpected creatures. For example, he could befriend a group of satyrs who are also outcasts and together they build a small, safe haven away from the typical demigod world. This type of fanfic often explores Percy's character in a more independent and self - reliant light, showing his growth without the direct influence of Chiron or his friends at Camp Half - Blood.
One plot idea could be Percy seeking Hestia's guidance during a time of great turmoil in the demigod world. Hestia, being the goddess of the hearth, could offer him a sense of home and stability in a chaotic situation. Another idea is a story where Hestia tasks Percy with protecting an ancient relic related to the hearth that has the power to either save or destroy the camp. Or perhaps a fanfiction where Percy discovers a long - lost connection between his family and Hestia, which gives him new powers or a special mission.
Perhaps the monster is from a different pantheon and is raising Percy to bridge the gap between two different mythologies. Percy then has to deal with the cultural shock and the politics of two very different mythological worlds while being raised by this strange being.
One possible plot twist could be that she discovers she has a different parentage than she thought. Maybe Hades isn't really her father, but someone else who had a reason to leave her with Hades. Another twist could be that she has to fight against Hades at some point, even though he raised her.
One interesting plot twist could be that a character thought to be an enemy turns out to be a long - lost ally. Maybe a cursed book reveals a prophecy that changes everyone's perception of the character's true nature.
One interesting plot twist could be a character who was thought to be an enemy turns out to be a secret ally. For example, a minor god who was initially seen as working against the demigods actually has a hidden agenda to protect them from a greater threat that the main Olympians are unaware of.
Perhaps a plot twist where Percy discovers that his own powers are somehow linked to the Bane in a way he never expected. Like his ability to control water is actually being manipulated by the Bane to cause chaos in the ocean realm, which would put him in a really difficult position of having to figure out how to break that connection while still using his powers.