Is there any interesting plot in 'harry potter has a big sister fanfiction'?

One idea could be that Harry's little sister has a unique magical ability that no one else in the family has. For example, she might be able to communicate with magical creatures in a way that even Hagrid is impressed by. This could lead to all sorts of adventures where she helps solve problems in the wizarding world using this special skill.

Yes, there are quite a few. Some explore how a sister would change the dynamic of Harry's family and his adventures at Hogwarts. For example, she might be an additional source of support for Harry or have her own unique magical abilities that come into play during the fight against Voldemort.

Emma Watson could be a great choice. Since she already has experience in the Harry Potter world as Hermione, she could bring a lot of charm and talent to the role of the big sister. She has the acting skills to portray the protective and magical nature of the character.

One possible plot could be that his girlfriend is a transfer student from a different wizarding school. She stands out not only because of her size but also her unique magical abilities. Harry is initially intrigued by her and they start a friendship that gradually turns into a relationship as they face various magical threats together.

The plot might revolve around the older sister being a part of a prophecy too. Just like Harry, she has a special destiny. But instead of being in the spotlight like Harry, she works behind the scenes to ensure Harry's success in the fight against Voldemort. She could be the one who finds out about Horcruxes first and guides Harry in that direction, all while dealing with her own challenges at Hogwarts, like trying to keep her identity as Harry's sister a secret from the wrong people.

Maybe the twin sister is sorted into a different house than Harry. This would cause a bit of a rift at first as they have to adjust to different house cultures. But in the end, they learn to combine the strengths of their respective houses to overcome a great threat to Hogwarts.

No, such fanfiction would be highly inappropriate and against the values and themes of the Harry Potter universe.

A possible plot development is that the two worlds start to merge because of their connection. Harry Potter's presence as Sesshomaru's sister could be the catalyst for this. As the worlds merge, new species and magic could emerge. They would have to deal with the chaos that comes with it, like how different cultures and magic systems interact. There could also be a sub - plot about Harry Potter trying to find a way back to her own world while still fulfilling her role as Sesshomaru's sister in his world.

Perhaps Harry's sister was kidnapped as a baby and raised by Death Eaters. She grows up believing in their cause until she discovers the truth about her family. This creates an internal struggle for her. She has to break free from the indoctrination and find a way to reconnect with Harry and the good side. Along the way, she might use the dark magic she was taught in a new and unexpected way to defeat Voldemort, like using a curse against him that he never expected because it was one of his own teachings.

One possible plot could be that the butler is actually a wizard in disguise who has been sent to protect Harry. He could use his knowledge of the wizarding and Muggle worlds to keep Harry safe from both magical threats like Death Eaters and Muggle dangers. For example, he could use his connections in the Muggle world to find safe houses for Harry when he needs to hide from Voldemort.