She could also be a key figure in the political intrigue of Camelot. As Arthur's sister, she has a certain status. There might be those who try to use her to get to Arthur or undermine his rule. So she has to navigate the dangerous world of court politics, using her wits and charm to outwit her enemies and protect Arthur and Camelot.
She could be very brave. Growing up in Arthur's shadow, she might feel the need to prove herself just as worthy. So when faced with danger, she doesn't cower but stands up and fights, whether it's against a magical beast or a political enemy.
There are also fanfictions where the OC is a commoner with a hidden noble lineage. In this story, as they interact with Arthur, they gradually discover their true heritage. This kind of plot often involves a lot of character development for both the OC and Arthur as they navigate through their new relationship while dealing with the court politics and the threat of Morgana.
One interesting plot could be her going on adventures with Natsu and his friends. She might have unique magical abilities that help the group in their quests.
One interesting plot could be Hisoka's sister getting involved in the Hunter Exam. She might use her unique skills, perhaps some that are similar to Hisoka's but with her own twist, to navigate through the challenges. For example, she could have a special ability to read opponents' intentions like Hisoka, but she uses it in a more empathetic way to avoid fights when possible.
One interesting plot could be that Gaara's little sister has a special power that she has to keep hidden from the village at first. This creates a lot of mystery and tension as she tries to navigate her life without being discovered.
Arthur Pendragon might fall in love with a noblewoman from a neighboring kingdom. Their kingdoms have a long - standing alliance. They meet at a grand ball held to strengthen the bond between the two lands. Arthur is immediately drawn to her grace and intelligence. They start writing letters to each other when she returns to her kingdom. Their love blossoms through these letters, but political intrigues and power - hungry lords try to break their relationship apart as they fear the united front of the two kingdoms through their love.
One interesting Arthur Pendragon OC fanfic could be about an OC who is a powerful sorcerer from a far - off land coming to Camelot. They initially face suspicion but end up helping Arthur in a great battle, using their unique magic skills. This kind of story can add new elements to the Arthurian legend.
In some fanfictions, the heir of Arthur Pendragon could have a special connection to the magical creatures in the Harry Potter universe. Since Arthur was a great king, the heir might inherit his ability to communicate or form bonds with these creatures. This connection could be crucial in solving various mysteries in the wizarding world, like finding a hidden place where a powerful dark magic object is hidden. They could use the help of these creatures to outwit the villains who are also after the same object.
Maybe Arthur Pendragon gets transported to the Fate world and his presence disrupts the normal balance of power. The mages in the Fate universe might see him as a threat or an opportunity. He could end up being a wild card in the Grail War, not bound by the normal rules of Servant summoning. His noble phantasm, Excalibur, could be a game - changer in battles against other powerful Servants.
One possible plot could be that the sister gets into some serious trouble in the Vampire Diaries world, like unknowingly making a deal with a vampire that endangers the family. Her older sibling decides to spank her as a form of punishment to teach her about the dangers. Another could be that she breaks a family heirloom that has some sort of protection spell in the vampire - filled town, and the spanking is more about her learning respect for the family's heritage in this supernatural context.