You can also explore the impact on the relationships within the Vampire Diaries universe. Maybe the sister was in a relationship before the amnesia. Now, her partner has to deal with her not remembering their love. It could lead to some really interesting plot twists, like the partner having to fall in love with her all over again while she discovers new aspects of herself.
A plot idea could be that the sister has amnesia due to a vampire - related incident. Maybe she was bitten by a new type of vampire that causes memory loss. The other characters then have to find a cure while also protecting her from other threats in the vampire world.
Well, you can try searching on fanfiction websites like Archive of Our Own. There are likely many stories with this theme there. Just type in the relevant keywords in the search bar and browse through the results.
The OC sister can be developed by showing her initial naivete. For example, at the start, she trusts her siblings completely. Then, when the betrayal occurs, her personality could shift to become more cynical. We can see her grow by having her learn new skills like self - defense or magic in order to protect herself from her siblings.
In such fanfiction, the relationship between the siblings can be complex. The act of spanking can be seen as a form of tough love. The older sibling might be very protective and spank the little sister to keep her out of harm's way in the dangerous Vampire Diaries world. It shows a sense of authority and care at the same time.
The drugged sister could start off as a very vulnerable character. But as the story progresses, she could develop a sort of inner strength. For example, she might initially be terrified of the vampires and the strange things she's experiencing due to the drug. But then, she could learn to use the drug - induced changes in her perception to her advantage, like being able to sense when a vampire is near even before they show up.
One common theme is loyalty. Sisters in the fanfiction often show unwavering loyalty to each other despite the supernatural challenges they face. Another is sacrifice. They might be willing to sacrifice their own happiness or safety for their sister. For example, in many stories, a sister will put herself in danger to protect her sibling from a vampire or a witch's curse.
In Vampire Diaries fanfiction, the concept of a twin sister sacrifice can add a whole new layer of drama. It could be related to some dark magic ritual where a twin's sacrifice is needed to gain power or break a curse. For example, perhaps a powerful vampire or witch demands it to achieve immortality or to control the supernatural elements in Mystic Falls.
One common theme is family loyalty. The sisters often have to stick together in the face of the many threats in the vampire - filled world. Another is power struggles. The sisters may have unique powers that others want to control or use for their own gains.
A common plot element is the mystery surrounding the amnesia. Usually, the 'ofc' (original female character) has no memory of important events, and the vampires in the story are often involved in either causing or trying to reverse it. For example, a vampire might have compelled her to forget something crucial, and the story then unfolds as she tries to piece her past back together.
There's also a character named Sophia in some fanfictions. Sophia is written as very intelligent. She uses her wits to outsmart her family's enemies. She has a great relationship with her brothers, especially Klaus. They have a deep bond that is explored in the fanfiction, and she often helps him see reason when he's about to make a rash decision.