Their relationship could develop uniquely by having them communicate through a special bond that is exclusive to their futa state. This bond allows them to share thoughts and feelings more deeply than normal, which in turn brings them closer together.
The relationship could be developed through a mutual goal of protecting someone or something. For example, they could both be on a mission to protect a group of humans from other dangerous vampires. Working together towards this goal would build trust and understanding between them, and as they face various challenges along the way, their love for each other would grow in a more complex and interesting way.
Maybe Carlisle and Bella could bond over their shared experiences of being different from the norm. Carlisle is a 'vegetarian' vampire, and Bella is a human who is in love with a vampire. They could have deep conversations about how they both struggle to fit in with their respective worlds and find solace in each other's understanding. This would add a new layer to their relationship and make it more unique.
One common theme is the exploration of their relationship. It could be a romantic relationship, showing how they interact and fall in love. Another theme might be adventure, where they go on some sort of journey together, facing challenges and growing closer through it.
Their relationship could be developed uniquely by having them communicate in a special way. For instance, instead of just talking, they have a mental connection that only they share. This connection allows them to understand each other's feelings and thoughts deeply, which helps them face the challenges in the gp.
One more way is if Bella is an artist. She starts painting portraits of the Lost Boys without knowing their true nature at first. When David sees her paintings, he is drawn to her creativity and the way she seems to capture their essence. This leads to a series of interactions where they slowly open up to each other, with Bella gradually accepting David's vampire world while David discovers the beauty in Bella's art and her human side.
The relationship could be developed uniquely by having Sabine's futa nature play a role in their communication. For example, she might have a different way of expressing emotions or intentions because of it. Ezra could learn to understand this new aspect of her, and it could bring them closer together.
One way to develop their relationship uniquely is to put them in a situation where they have to protect each other's secrets. For example, Jasper might have a secret from his past as a vampire in the military, and Bella has her own secrets about her relationship with the wolves. By relying on each other to keep these secrets, a strong bond forms between them.
To develop Roseline uniquely, you could give her an unusual hobby like collecting antique keys. This hobby could tie into the story in some way, like leading to a mystery she and Bella have to solve. For Bella, you could make her really good at parkour, which gives her a different kind of physicality and confidence. When they face challenges, their skills can play important roles.
I'm sorry, but I can't recommend such fanfiction directly as it may involve inappropriate or non - mainstream content. However, you can try searching on some general fanfiction platforms like Archive of Our Own and use their search filters to look for positive and appropriate stories about Bella and Rosalie.
One plot idea could be that Rosalie and Bella discover a hidden power within their futa forms that is connected to the supernatural world around them. They then have to navigate how to use this power while also dealing with the reactions of their friends and family in the Twilight universe.