No. Writing 'smut' (pornographic or sexually explicit) fanfic involving characters from the Harry Potter series is inappropriate. The Harry Potter franchise is aimed at a wide audience including children and young adults, and such content goes against the family - friendly and magical essence of the original work.
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.
It changes the family dynamic. Instead of being an only child, Harry now has a sister, which means there's more family support or potential family drama. For instance, the sister could be a target of Voldemort too, adding another layer of danger.
One common theme is the struggle against the Slytherin stereotype. The sister character often has to deal with the perception that all Slytherins are evil or dark - wizards - in - training. For example, in many fanfics, she might be really kind - hearted but is constantly judged by others because of her house.
The twins themselves are often great characters in these fanfics. Their mischievous nature and loyalty to their sister add a lot of fun and heart to the story. The sister, of course, is a central character with her own unique personality and abilities.
One popular 'Harry Potter sister fanfic' is 'The Lost Potter Sister'. It often features a long - lost sister of Harry Potter who discovers her true identity and her connection to the wizarding world. Another one could be 'Potter's Hidden Sister', where the sister has unique magical abilities that set her apart from the other characters in the Harry Potter universe.
Common themes include love and loyalty. The twin sister's love for her brother and her loyalty to him and their friends is a central aspect. There's also the theme of discovery. Discovering new spells, new places in the wizarding world, and even new aspects of their family history. And of course, the theme of good versus evil. Just like in the original Harry Potter series, the twin sister has to take a stand against Voldemort and his followers. In some fanfics, she might have a different approach to fighting evil compared to Harry, which makes for an interesting read.
In many 'Harry Potter sister fanfic' stories, the sister's character is developed through her relationships. She could have a complex relationship with Harry, maybe starting off as jealous of his fame but then growing to support him. Or she might form a really close bond with Hermione, learning from her and becoming a strong female character in her own right. Her character also develops as she faces challenges in the wizarding world, like dealing with discrimination because she's a Potter. These experiences shape her into a more confident and powerful witch.
There should not be any such fanfic. The Harry Potter series is about friendship, courage and magic, not about abuse. This kind of concept goes against the positive values that the original work promotes. It is also unethical and can be very disturbing to the fans who love the original story.
In some fanfictions, it could be through powerful magic spells that he discovers or is taught. Maybe he stumbles upon an ancient spell in the restricted section of the library that allows him to summon a family member. Another possibility is that he unknowingly activates some kind of magical artifact that has the power to bring a sister into his life.