Well, one unique plotline could be her relationship with her father, Hades. In some fanfics, she might be trying to earn his respect in a different way than a male Percy would. For example, she could use her femininity to her advantage in the Underworld politics.
You can start by giving her a distinct personality. Maybe she's shy because she's always been feared for her father's sake. Then, gradually show her growing confidence as she discovers her own strengths. For example, if she has the power to raise small skeletons as minions, at first she's scared of it, but later she learns to use it for good. Also, explore her relationships with other characters. Her friendship with Percy could be based on mutual understanding of being different among the demigods.
The main characters are Percy and Fem Hades. Percy is the protagonist from the original series, and in the fanfiction, his story continues with his interactions with Fem Hades. Fem Hades, on the other hand, is a unique take on the Hades character. She could have different personality traits compared to the male Hades in the original mythology. There might be other characters that are introduced as the story progresses, but these two are the foundation of most Percy Jackson and Fem Hades fanfiction.
One interesting plot could be Fem Hades helping Percy on a quest in the Underworld. Maybe she uses her unique powers as a female version of Hades to guide him through dangerous areas that are usually off - limits to normal demigods.
I've come across a fanfiction titled 'The Daughter of Aphrodite's Quest'. In this story, the fem Percy Jackson embarks on a quest that is intertwined with matters of the heart and heroism. It delves deep into her character, exploring how being a daughter of Aphrodite influences her decisions. Additionally, 'Charm and Courage' is a fanfic where she uses her Aphrodite - side to her advantage in the face of great danger, making for an exciting read.
I really liked 'Fem Percy: Hades' Legacy'. It delved into her powers as the daughter of Hades. Since she's female, she might use her powers in a different way than the original Percy. She could be more in tune with the underworld's female spirits and use that connection to her advantage in battles and quests.
To develop her character, start with her appearance. Maybe she has dark, almost black hair like the shadows of the Underworld and pale skin. For her personality, she could be a bit of an outcast among the other demigods due to her father. This might make her a bit brooding but also determined to prove herself. Give her some quirks, like she always wears a small charm that was a gift from Hades.
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.
She is usually depicted as a bit of an outcast among the demigods. Because of her connection to the Underworld, which is seen as a dark and spooky place, other demigods might be afraid or distrustful of her. But this also makes her a very independent and self - reliant character in fanfics.
One great fanfic could be where the Daughter of Hades has to deal with the stigma of her parentage among the other demigods. She might struggle to fit in, like trying to participate in camp activities while others are a bit wary of her powers related to the Underworld.