The fanfic could start with Blake being bitten by a vampire - like creature during a solo mission. As she slowly turns, she starts to have visions of an ancient war between vampires and some powerful beings in Remnant's past. Yang, Ruby, and Weiss notice her changes and set out to find a cure. Along the way, they learn more about Remnant's history and the true nature of the vampire infection, which might be related to some sort of powerful magic or ancient technology.
When writing a RWBY vampire infection fanfic, start with a strong hook. Maybe open with a scene where a character wakes up in a strange place, already infected and not knowing how it happened. Then, research vampire lore. You can incorporate elements like a vampire's weakness to sunlight or silver into the RWBY universe in an interesting way. For instance, in Remnant, maybe vampires are weak against Dust of a certain type. Finally, have a clear plot structure. Decide whether the fanfic will be about finding a cure, or about the characters learning to live with the infection, and build the story around that goal.
One idea could be a fanfic that explores the backstories of minor characters in RWBY more deeply. For example, you could focus on a character like Velvet and create a story about her training before coming to Beacon. Another could be a crossover within the RWBY universe itself, like a team-up between different schools' teams that we haven't seen much of in the official series.
Maybe it involves the characters reminiscing about their time at Beacon Academy. They could think about the classes they took, the friends they made outside their teams. Like Weiss remembering her struggles with fitting in among students from different backgrounds, and how those experiences shaped her.
The combination of RWBY's unique world and vampire lore. RWBY has its own set of rules regarding combat, Aura, and Semblance. When you add vampire elements, like their immortality, super strength, and blood - sucking abilities, it creates a whole new set of possibilities for stories. For example, a vampire character might have an unusual Semblance or interact with the existing RWBY characters in unexpected ways.
One idea could be a story where Velvet discovers a new type of Grimm with unique abilities. She then has to figure out how to combat it, using her skills and the help of her friends. Maybe she could study the Grimm's behavior and weaknesses in secret to surprise everyone when she reveals her knowledge.
Maybe a fanfic where Weiss discovers a hidden Faunus community while exploring. She gets separated from her team and has to rely on the Faunus there to survive. This experience makes her re - evaluate her thoughts on Faunus. The Faunus in the community could have unique cultures and abilities that Weiss has never seen before, and she becomes fascinated by them.
One idea could be Ruby discovers a new form of nanotech in a hidden part of Remnant. This nanotech could enhance her Crescent Rose, giving it new abilities like shape - shifting or self - repair.
One common theme could be the struggle against the fungal infection. Characters in RWBY might be shown fighting not only their usual foes but also this new threat of the fungal infection. It could also explore themes of survival, as they try to find a way to stop the spread or cure the infected. Another theme could be the impact on the relationships between the characters. For example, if a team member gets infected, it can put a strain on the team dynamic as they have to decide whether to try and save the infected or protect themselves from the spreading infection.
In a fanfic, Ash could be turned into a vampire by an ancient, powerful Pokemon with vampiric abilities. This would completely change his relationship with his other Pokemon. Some might be scared of him, while others would stay by his side. He would then have to learn to control his vampire powers and instincts in order to continue his journey. For example, he'd need to figure out how to be in the sunlight without getting burned as he travels from place to place.
Another concept is a crossover of the powers. In the fanfic, Weiss could have some sort of ice - based kagune, which combines her Schnee family glyph powers with the unique abilities of a Tokyo Ghoul. Blake could use her shadow powers in a way that is similar to how ghouls move in the shadows, making her a more stealthy fighter in the Tokyo Ghoul setting.