Perhaps at first, their relationship is one of suspicion, especially if they come from different backgrounds or have different agendas in the fanfiction. But as Bella's sickness progresses and they are forced to interact more, they gradually find common ground and their relationship evolves into a friendship or something more.
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.
Their relationship might develop as they take care of each other while being sick. Asta, being his usual selfless self, would try his best to make Noelle comfortable. This could make Noelle see Asta in a new light and grow closer to him.
After the kiss, they might become closer friends. They could start to confide in each other more. For instance, Bella might share her insecurities about being human among the vampires with Alice more openly, and Alice could share more of her visions that are related to Bella's future.
It often starts with attraction. Edward is drawn to Bella's unique scent and her differentness. Bella, on the other hand, is intrigued by Edward's mysterious nature.
Tanya and Bella might be characters from a popular book or movie series that the author of the fanfiction really likes. For instance, they could be from a vampire - related series, where the actions like handcuffing could be related to the power dynamics or the complex relationships within that world. They could also be from a mystery or thriller - type of story, where this act is part of a larger mystery or plot twist.
In fanfiction, their relationship might start to develop when they have to face a common enemy. Let's say there's a rival football team that tries to play dirty against them. Bella and Zach would need to rely on each other's strengths, Zach's physical skills on the field and Bella's strategic thinking. As they work together to overcome this threat, they start to respect and like each other more. This respect could then turn into deeper feelings as they spend more time together off the field too, like studying together for school or just hanging out with friends. They might start to notice little things about each other that they find endearing, like the way Zach always ties his shoelaces in a double knot before a game or how Bella bites her lip when she's thinking really hard about a play. And slowly but surely, their relationship would grow from just being teammates to something more special.
They could be two characters who are part of a unique group in the GP fanfiction world. Maybe they are rivals within the group, and this act of tying Bella to the bed is a way for Tanya to assert some sort of dominance or get back at Bella for something.
Their relationship might start off as just guild mates. But as they work together on more and more quests, they could develop a deeper respect for each other. For instance, Lucy might be initially intimidated by Cana Lemon's brash nature, but as she gets to know her better, she realizes there's a lot more to her.
Bella could become more independent. With Paul leaving, she has no choice but to rely on herself. She might become more assertive in making decisions for herself and her unborn child.
One idea could be that Tanya tries to use her unique abilities to heal Bella. Since Tanya is often depicted as having certain powers in related stories, this could be a central plot point where she battles against Bella's unknown illness.