Blake Belladonna is quite popular in RWBY Kaiju fanfiction. Her stealth abilities can add an exciting element when she has to sneak around a kaiju or gather intel on it. Yang Xiao Long is another favorite. Her powerful punches could be portrayed as being able to at least stun a kaiju for a short time, and her fearless attitude makes her a great character to face these huge monsters. Also, characters like Qrow Branwen might be popular as they can bring in their experience and unique skills to deal with the kaiju situation.
The main character, Kafka, is often a popular one in fanfiction. Writers might put him in various new situations or develop his character further, like exploring his emotions more deeply during battles.
Often, the main human protagonists who are brave and resourceful are popular. For example, a fearless military general who leads the fight against the Kaiju. Also, any character with a special ability like a scientist who can understand the Kaiju's behavior.
One interesting idea could be the RWBY characters having to team up in new ways to combat the kaiju. For example, Ruby's speed might be used to quickly dodge a kaiju's attacks and find its weak spots. Another idea is the fusion of Dust technology with kaiju - like elements. Maybe they create new weapons that can both harm the kaiju and also harness some of their power. Also, the idea of kaiju having Aura or semblances of their own could be really cool, changing the dynamics of how the RWBY characters interact with them.
Some of the lesser - known Kaiju can also be interesting to include in fanfiction. For example, Rodan. He has his own unique abilities and personality. A fanfiction could explore his backstory more deeply, or create a new relationship between him and the other more well - known Kaiju. Anguirus is another one. He could be portrayed as a loyal ally to Godzilla, or have his own motives for being involved in the Kaiju Wars.
Kafka Hibino is often a popular character in fanfics. His transformation into a kaiju - like form and his struggles to control it make for great storytelling. Writers can explore his inner thoughts and how he copes with his new abilities.
One popular character might be a kaiju girl with the ability to fly. Her aerial battles against other kaiju or threats are often a highlight in many fanfics. She is usually depicted as strong and independent.
New original characters created specifically for the fanfiction can also become popular. For instance, a character who is a Kaiju whisperer, someone who can understand and communicate with Kaiju. This character can bring a whole new dynamic to the relationship between humans and Kaiju in the fanfiction world.
Weiss Schnee can be a great character in shapeshifter fanfictions too. Her family's connection to the Schnee Dust Company could lead to some interesting plotlines where she shapeshifts to access hidden knowledge or powers related to Dust, perhaps into a form that can better manipulate Dust than she already can.
Ruby Rose is often a popular character in RWBY Wolf fanfiction. Her speed and combat skills can be incorporated into stories involving wolves in creative ways, like racing against a wolf - Grimm or using her scythe to fend off a pack of wolf - like enemies.
Blake is often used in these fanfictions. Her stealthy nature could be utilized in a game where she has to infiltrate an enemy base within the game world. Her relationship with other characters also adds depth to the story when they're all involved in a gaming adventure.