One idea could be that the twin sister has a different combat style. For example, while Weiss uses her Glyphs mainly for ice attacks and movement, the twin sister could use Glyphs for illusions. Maybe she was separated from Weiss at a young age due to some family drama or a Grimm attack. As the story progresses, they cross paths during a major battle against Salem's forces and initially don't recognize each other. But then, through some shared memories or a family heirloom, they figure out their relation and team up to defeat the common enemy.
She would definitely have an impact on Weiss's relationship with Ruby. Ruby would be curious about the new addition and might try to befriend the twin sister. This could cause some jealousy in Weiss at first as she feels Ruby's attention is being divided. But over time, they would all form a stronger bond. With Blake and Yang, the twin sister could bring new perspectives. For example, she might have different views on the Faunus situation which could either create some tension or lead to better understanding among them.
One great Weiss twin fanfiction is 'The Twin Bond'. It delves into the relationship between Weiss and her twin in a very emotional way. The author does an amazing job of exploring how they interact, their shared past, and how they face challenges together. It also has some really cool fight scenes that are well - written and fit into the RWBY universe.
First, you need to really understand Weiss's character. Know her strengths, weaknesses, and her backstory in the RWBY world. Then, when creating the twin, make sure they have distinct but related characteristics. For example, if Weiss is more reserved, the twin could be more outgoing but still share the same sense of justice. Also, have a clear plot that involves both of them, like a shared quest or a mystery to solve.
One common theme is sisterly bond. The fanfictions usually explore the deep connection between the twin sisters, how they support each other through tough times. Another theme is self - discovery. The sisters often embark on a journey to find out who they really are.
Love and friendship are also common themes. The relationship between the twin sisters can be seen as a deep friendship as well as a family bond. And in some stories, they might both fall in love, but in different ways, which could lead to some interesting plot twists. There could also be a theme of self - discovery, where the presence of the twin sister helps Blake discover new aspects of herself she didn't know before.
One popular 'rwby twin sister fanfiction' is 'The Twin Sisters of Beacon'. It follows the adventures of two sisters at Beacon Academy with unique powers and personalities. Another one could be 'Twin Bond in RWBY', which focuses on the special connection between the twin sisters as they face various challenges in the RWBY universe.
I really like 'Weiss and the Faunus Bond'. In this fanfiction, Weiss discovers the unique aspects of Faunus culture through her interactions. It shows her growth as a character as she overcomes her initial prejudices. It also has some great action scenes intertwined with the emotional development.
This fanfiction concept could also explore the relationship between Weiss and Raven. Raven is a complex character, and her training of Weiss could lead to some deep conversations and exchanges of ideas. It could be a way to show Weiss's growth in understanding different perspectives within the RWBY universe.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3). There are often many RWBY - related fanfics there, and by using the keywords 'rwby jealous weiss' in the search bar, you should be able to find relevant stories. Another option is Fanfiction.net, which also has a large collection of RWBY fanfiction.