A common theme could be the clash of different mythologies. Since Sigurd and Brynhildr are from Norse mythology (in the context of Fate) and RWBY has its own kind of lore, seeing how these different mythological elements interact is often explored. For example, how their powers might be perceived in the RWBY world of Huntsmen and Grimm.
I'm not sure of specific 'Sigurd and Brynhildr Fate RWBY Fanfiction' off the top of my head. But you could also try reaching out to RWBY or Fate fan communities on social media platforms. Reddit, for example, has dedicated subreddits for both fandoms. Post a request there asking for good fanfictions involving these two characters in the RWBY world. People in those communities are usually quite helpful in sharing their favorite reads.
Theirs is a relationship full of passion and conflict. Their love is intense, which makes it interesting. And the fact that they are often caught up in the grand schemes of fate in the Fate universe adds an extra layer of drama.
One common theme is the exploration of different powers. Since both RWBY and Fate Stay have their own unique power systems, fanfictions often play around with how these powers interact. For instance, the semblances in RWBY and the magic in Fate Stay can be combined in various ways.
Well, in 'After Fate RWBY Fanfiction', a prevalent theme is identity. Characters from both universes might question their identities when the two worlds collide. For example, a RWBY character who gets involved with Fate magic might wonder if they are still the same person or if they are becoming something new. Also, the theme of friendship and teamwork is often explored. In these crossovers, the characters have to learn to work together, despite their differences in origin and abilities, to face new threats that come from the combination of the two universes.
One common theme is the clash of cultures. The two universes have very different settings and ways of life. So, fanfictions often explore how the characters adapt to this new environment. For example, a character from Fate Stay Night might be shocked by the technology in RWBY.
In some fanfics, it's a love story. Writers might focus on the moments when they first meet and fall in love. They might describe how Sigurd's heroic deeds attract Brynhildr, and how their connection is so strong that it defies the odds. However, it's also common for it to become a tragedy as the darker elements of the Fate universe start to play their part.
One of the main themes is sacrifice. The characters often have to make difficult choices that involve sacrificing something, whether it's their own safety or their relationships. Another theme is the search for identity. Many of the characters are trying to figure out who they really are, especially those with special powers.
A good plot for a Brynhildr Fate fanfic could be a time - travel story. Brynhildr could be sent back in time to a crucial moment in her own history. She could then have the chance to change things that she regretted in her past. Or, you could write about Brynhildr falling in love with a character who is not from her original story. This would create a lot of interesting drama as she tries to balance her new feelings with her duties as a Servant. Also, a story where Brynhildr has to train a new and inexperienced Servant could be quite engaging.
One of the common themes is redemption. There are characters in the movies who have done wrong things and in fanfictions, they might be on a path to redeem themselves. Also, loyalty is a big theme. The loyalty among the crew in the movies is further explored and sometimes tested in fan - created stories. And of course, the theme of love and relationships, not just romantic but also the platonic relationships between the characters.