Another important character that is often involved is Hagrid. He might be the one who stumbles upon the forgotten twin sister in her hiding place or he could be the one to introduce her to the wizarding world properly. Then there are the Weasley family members. They could play different roles, like Ginny might become the twin sister's best friend or Fred and George could include her in their pranks and adventures, adding some light - heartedness to the story.
Well, obviously Harry Potter is one of the main characters. His twin sister would be another main character. There might also be the usual suspects from the original series like Hermione and Ron, who would likely be involved in the story as friends and comrades to Harry and his sister. Dumbledore would probably also play an important role as he does in the original books, guiding and protecting the young wizards.
Severus Snape is often a prominent character in these fanfictions. His complex relationship with the Potter family could be explored further. He might have a different attitude towards the twin sister, perhaps seeing in her some qualities that remind him of Lily Potter. This could lead to some interesting interactions and plot developments, like him secretly protecting her or teaching her some advanced potions techniques. Dumbledore is also popular. His all - knowing and guiding role can be enhanced in the fanfiction, as he might have special plans for the twin sister in the fight against Voldemort.
Ron and Hermione are likely to interact with them. Ron might be a bit more protective of the sister, while Hermione would probably study and share knowledge with her. They could all be in the Gryffindor common room, discussing spells and strategies.
Luna Lovegood is also quite popular in these fanfictions. She and the twin sister could bond over their shared belief in things that others might find strange. They might go on adventures in the Forbidden Forest together, looking for the Crumple - Horned Snorkack. And of course, Ron is always a key character. He could be like a big brother to the twin sister, and they could have a lot of funny moments together, especially when it comes to food at Hogwarts.
Ron could also play an important role. He could be a bit jealous at first of the close bond between Harry and his sister, but then they become friends. Ron's sense of humor and loyalty would make him a fun addition. He could be involved in their adventures, like when they go looking for Horcruxes, and provide some comical relief during tense times.
One interesting plotline could be the twin sister having hidden magical powers that are different from Harry's. For example, she might have an affinity for ancient spells that have been long forgotten in the wizarding world. Another could be that she was separated from Harry at birth due to a prophecy that the dark forces were after her specifically, and she grows up in a different magical community, unaware of her true identity until later in the story.
Then there's their parents. In the fanfiction, the mother could be a key figure as the one carrying the sister in the womb. Her experiences during pregnancy might be detailed, like any strange feelings or dreams she had. And the father, who might be involved in protecting the family during this time when the sister is in the womb. Their family bond is often an important aspect in these stories.
You can start by giving her a distinct personality. If Harry is brave and impulsive, she could be more cautious and thoughtful. This would create an interesting contrast between them. Also, give her some unique hobbies or interests, like she's really into ancient runes or potion - making. This will make her a more well - rounded character.
Hermione would still be a very popular character. She could be the one to help the twin sister study and understand the more complex aspects of magic. Her logical thinking and vast knowledge of magic would be invaluable in their adventures.
A really interesting one is 'A Twin's Tale'. In this fanfic, the twin sister has her own unique powers and personality. It's fascinating to see how she interacts with the other characters like Hermione and Ron. The story also explores how her presence changes the events in Hogwarts and in the fight against Voldemort. It's a must - read for any Harry Potter fanfiction lover.