One idea could be that the Grimm in RWBY are somehow related to the beasts in Bloodborne. Maybe there's a common origin or a dark force that controls both. For example, the Grimm could be an earlier form of the Bloodborne beasts, and the Huntsmen and Huntresses have to deal with a new type of Grimm that has the characteristics of the Bloodborne creatures, like a more sentient and intelligent type of Grimm.
One unique feature is the blend of different art styles. Bloodborne has a very dark, gothic, and somewhat medieval - inspired art style, while RWBY has a more modern, anime - like style. In the crossover fanfiction, these two styles can create a really interesting visual in the reader's mind when they imagine the story.
Sinister characters like Adam Taurus from RWBY could also be interesting in a Bloodborne crossover. His already dark and violent nature could be enhanced in the Bloodborne setting. He could form alliances with some of the more sinister forces in Bloodborne, or perhaps he becomes a sort of anti - hero, fighting against the greater evils in the Bloodborne world while still being a morally ambiguous figure.
The unique settings that result from the crossovers are also a big draw. When Bloodborne crosses with 'Metroid', you might have a scenario where the hunters are exploring the alien landscapes of the Metroid world. The combination of Bloodborne's gothic architecture and Metroid's sci - fi environments makes for a visually and conceptually exciting read. It can also introduce new gameplay - like elements into the story as the characters adapt to the new settings.
There's also 'RWBY in Bloodborne's World'. This fanfiction takes the RWBY characters and drops them into the terrifying and mysterious setting of Bloodborne. It's great for those who like to see how different characters adapt to a new and dangerous environment. It often has some intense fight scenes as the RWBY girls use their skills against the nightmarish creatures of Bloodborne.
The plot could involve a crossover of the powers. In the world of Bloodborne, there are powerful blood-based abilities. Imagine if a character like Daenerys Targaryen got access to some of these powers. She could become even more of a force to be reckoned with, using the blood powers along with her dragons. It would change the power dynamics in Westeros completely.
Sure. One popular 'bloodborne crossover fanfic' is the one that crosses over with 'Dark Souls'. It combines the dark and gritty atmosphere of both games really well. The characters from Bloodborne are placed in the Dark Souls world and vice versa, creating interesting new storylines and interactions.
One common theme is the clash of different mythologies. For example, when Bloodborne crosses with other game universes, their respective mythologies about gods, monsters, and the afterlife collide.
A common element is often the merging of the two distinct worlds. For example, the unique weapons from RWBY might be combined with the dark and gothic atmosphere of Bloodborne. Also, the characters' abilities could be a mix. The OC (original character) might have traits from both universes, like a RWBY character with a Bloodborne - inspired power.
A way to explore madness in the crossover is by having a character from the Bloodborne world try to use the knowledge or power of the Old Ones. Since the Old Ones are so far beyond human understanding, this attempt could backfire horribly. The character might start to lose their grip on their identity, their memories becoming muddled with the strange knowledge of the Old Ones. This transformation into madness could be a central part of the fanfic's plot, as the other characters then have to deal with this once - sane individual who has now become a threat due to their new - found madness.