A common plotline is the OC helping Blake with her internal struggles. Blake has a lot of emotional baggage from her time in the White Fang and her experiences with discrimination. The OC could be someone who has also faced hardships and can offer a different perspective. They might go on a journey together, not just physically but also mentally, as Blake tries to come to terms with her past and the OC helps her along the way. In some fanfictions, the OC might also introduce Blake to a new group or culture within the RWBY universe, which then leads to new adventures and story developments.
One interesting plotline could be Sun's family welcoming Blake into their family. Maybe they have some traditional family activities that Blake has to get used to, like a special family gathering where they share stories of their past adventures. It could also involve Sun's family helping Blake deal with her own family issues or past traumas.
One interesting plotline could be Blake's search for redemption. Since she was once part of the White Fang, she might strive to make amends for the actions she was involved in or the things she witnessed. This could involve her going on solo missions to help those who were affected by the White Fang's more violent actions.
First, give your OC a clear backstory. If they're in a story with Blake, their past should somehow connect to the themes of RWBY. For example, if they were also affected by the actions of the White Fang, it creates an instant connection. Second, design a unique look and fighting style. This makes them stand out. For instance, if Blake has her sword and ribbon, your OC could have a weapon that's completely different, like a staff that can split into two swords. Third, give them a distinct personality. Maybe they're more outgoing than Blake, which can create interesting interactions. They should also have their own goals and dreams within the RWBY universe.
One common theme is the idea of finding acceptance. The OC often has to find their place in the RWBY world, and Blake is a part of that journey. For example, in many stories, the OC may be an outcast like Blake was, and they bond over their shared experiences of not quite fitting in.
One possible plotline could be Ruby and Blake facing a difficult mission together. During this, they realize their feelings for each other are deeper than friendship. They might have to protect each other from powerful enemies, and through these shared experiences, their love blossoms.
Well, the theme of acceptance is quite prevalent. The OC sibling may be different in some way, like having unique abilities or a different background, and they have to be accepted by Blake and the other RWBY characters. Also, the theme of sacrifice often comes up. The sibling might sacrifice their own desires or opportunities for the sake of Blake or the greater good in Remnant. In some fanfictions, this sacrifice can be very emotional and impactful.
One popular Blake Mark RWBY fanfic could be 'Blake and Mark's Adventure in Remnant'. It might involve them going on quests together, facing Grimm and uncovering secrets of the world. Another could be 'Mark's Support for Blake', which focuses on how Mark helps Blake deal with her internal struggles and her role in the fight against Salem.
One popular theme is family. Since Raven is Yang's mother and Blake has her own complex family history, many fanfictions explore how their family experiences could either bring them together or drive them apart. For example, they might bond over the feeling of being an outsider in their own families at times.
One great piece of 'rwby blake sibling oc fanfiction' is 'Sibling Bonds in Remnant' which delves deep into the relationship between Blake and her new OC sibling. It shows how they face the challenges in the world of Remnant together. Another interesting one is 'The Hidden Sibling of Blake'. This fanfiction creates a unique backstory for the OC sibling and how they influence Blake's journey in RWBY.
Yes, there are likely several out there. You can start by looking on fanfiction platforms like Archive of Our Own (AO3). They usually have a wide range of RWBY fanfictions, and it's quite possible to find ones featuring Ruby and Blake in a romantic moment like a kiss.