Perhaps she's a sister who was thought to be dead but actually survived. She could have been corrupted by the experiences she had while being 'dead'. When she returns, she blames Percy for not saving her properly. This false blame leads her to betray Percy. She could start spreading rumors about Percy being a coward or a bad leader among the demigod community.
Yes, there might be. Fanfiction is a vast world where all kinds of crossovers and creative ideas are explored. You can start by looking on popular fanfiction websites like Archive of Our Own or FanFiction.net. Just search for the specific concept and see if any authors have written about it.
Well, one possibility could be that the sister discovers she has some unique powers that are different from Percy's. For example, she might be able to communicate with mythical creatures in a way that no one else can. This could lead to her getting involved in a quest to save a particular part of the mythical world that is in danger.
Her power could be related to healing. Since the demigods often get injured in their battles and adventures, having a healer in the family would be a great advantage. She could use her power to heal not only Percy but also other demigods. This would make her very popular in the camp and also attract the attention of the gods. Some gods might want to use her for their own purposes, while others might want to protect her because of her valuable gift.
She might start off as a shy character. But as the fanfiction progresses and she discovers her connection to lemons, she becomes more confident. For example, if she uses lemons to make a magical item, she realizes her own capabilities and starts to stand up for herself more.
A common theme is the discovery of the sister's powers. For example, she might find out she can control water like Percy but in a different way. This adds an interesting twist to the story as they learn to use their powers together.
I really like 'A Sister's Tale in the Percy Jackson Universe'. In this fanfiction, the sister character brings a new dynamic to the story. It shows how she copes with the knowledge of the Greek gods and her relationship with Percy, which is full of both love and typical sibling spats. It's a very engaging read.
One great 'Percy Jackson and Sister' fanfiction is 'The Lost Sister'. It has an interesting plot where the sister has unique powers and they go on adventures together. The character development is really well - done.
Perhaps a powerful sorceress from an ancient line that has a long - standing grudge against the demigods. She sees the sister as an easy target at first, but as the story progresses, she realizes that the sister is much stronger and more determined than she thought. So she becomes more and more desperate to defeat her and stop her from fulfilling her destiny.
One popular Percy Jackson sister fanfic is 'The Lost Sister'. It has an interesting plot where the sister discovers her powers and tries to fit into the demigod world. Another is 'Sister of the Sea' which focuses on the sister's connection to the ocean. And 'A Sister's Journey' shows the sister's adventures and how she overcomes various challenges in the Percy Jackson universe.