One possible plotline could be that Marcus discovers Bella's blindness and is initially hesitant about their relationship but then grows to see it as something that makes her unique and special. He might then become very protective of her.
A plotline could involve Bella's family's reaction to her relationship with Emmett. Given her blindness, they might be even more worried about her getting involved with someone like Emmett. Also, the fanfiction could show how Bella and Emmett communicate on a deeper level. Since she can't see, they might develop a stronger telepathic or emotional connection that is unique to their relationship.
One possible plotline could be that Bella and Marcus form an unexpected friendship. They might start sharing secrets and helping each other out in a world full of challenges. For example, Marcus could be in some kind of trouble and Bella uses her unique perspective or skills to get him out of it.
Another plot could be that they are on opposite sides of a conflict initially. But as they realize they are mates, they have to find a way to reconcile their differences and work together. This could involve a lot of internal struggle for both of them as they deal with loyalty to their respective sides and their new - found bond.
I'm sorry I don't have specific fanfiction stories to recommend directly. But you can try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net. Use the key phrases 'bella is marcus mate and bella is blind' in the search bar, and you might find some interesting stories there.
Power dynamics might also be a theme. Marcus may have certain powers or a position within the story's world, and how that affects his relationship with Bella could be explored. For example, if there are other characters who oppose their union because of Marcus' power or status. Another common theme could be the struggle against outside forces. There might be other characters or groups that try to keep Bella and Marcus apart, creating conflict and drama in the story.
One possible plotline could be the struggle against other vampires who oppose their relationship. Another might be Bella adjusting to the vampire world in a different way than in the original stories, with Damon as her guide. Maybe they go on adventures together to protect their relationship from various threats.
At first, it might be a bit rocky. Bella, being human and now blind, is in a very vulnerable state. Caius, as a powerful vampire, may come off as intimidating. But as time goes on, they start to develop a deep bond. Caius learns to be more gentle and caring, and Bella starts to trust him more and more.
I haven't read a specific one, but generally, it might start with Bella somehow being fated to Marcus. Their first encounter would be crucial, and then it could progress to them exploring their new bond. Maybe there are other vampires who oppose their union.
Well, Caius could be very possessive and see Bella's blindness as something that makes her even more his. He would be by her side all the time, guiding her physically when needed. He might also share his vampire senses with her in some way, like describing the world around them in vivid detail so that she can 'see' through his words. And he would definitely be very angry if anyone made fun of or took advantage of her blindness.
One good fanfiction could be 'Bella's New Bond with Marcus'. It might explore how their relationship as mates develops in a world filled with vampire politics. Another could be 'Bella and Marcus: A Forbidden Love', which delves into the challenges they face due to the existing vampire hierarchies.