Well, in this fanfiction plot, it could start with an unexpected encounter between Ichigo and Halibel. Maybe Halibel is injured in the human world and Ichigo helps her. This act of kindness makes Halibel see Ichigo in a new light. As they get closer, they realize they share a common goal of protecting the innocent. Their marriage could be a symbol of the union between the Soul Reapers and the Arrancars in a way. They could then go on adventures together, facing new threats and using their combined powers to keep both their worlds safe.
One possible plot could be that Ichigo and Halibel initially struggle to understand each other's worlds. Since Ichigo is from Karakura Town and Halibel is from Hueco Mundo. But as they spend more time together, they start to learn about each other's values and dreams. They might face opposition from their respective groups, like Ichigo's friends might be skeptical about his relationship with a former Arrancar. However, through their love, they gradually break down those barriers and build a new life together, perhaps even uniting the two worlds in some small way.
Ichigo would develop a more patient side. Halibel's different way of thinking and her more reserved nature would force Ichigo to slow down and really think about his actions. He would also become more protective, not just of Halibel but also of the new relationship they are building. Halibel would start to open up more. She was always a bit of an enigma in the original story. But in this fanfiction, being married to Ichigo would make her more expressive. She would start to share her thoughts and feelings more freely, and her character would become more complex as she tries to balance her old self with the new self that is influenced by Ichigo and his world.
For Ichigo, he could develop a more nuanced view of the Arrancars. Through his interactions with Halibel, he might realize that not all Arrancars are pure evil. This could make him more open - minded in his future encounters with other Hollows. As for Halibel, she could start to see the value in the Shinigami way, especially Ichigo's sense of justice. It might make her question her own loyalties and purpose.
Maybe in the fanfiction, Ichigo gets lost in Hueco Mundo and Halibel finds him. Instead of attacking, she decides to help him find his way back. During their journey, they encounter various challenges and secrets about Hueco Mundo are revealed to Ichigo through Halibel. This could lead to a new understanding between the two species they represent.
One plot idea could be that Ichigo and Halibel are forced to team up against a new, powerful enemy that threatens both their worlds. They start off distrusting each other but gradually learn to respect and rely on one another's strengths.
A plot could involve Halibel getting injured and being found by Ichigo. He takes her in and nurses her back to health. During this time, they have a chance to really talk and get to know each other on a deeper level. Their different worlds collide as they start to develop feelings for one another, but they also face challenges due to their different allegiances.
Well, a plot could involve a power - sharing situation. Maybe there's a power - draining curse in Hueco Mundo that affects both of them. In order to break it, they have to combine their powers in a way they never thought possible. This journey of trying to break the curse could make them see each other in a new light. They could also be involved in a mystery where they have to figure out who is behind a series of disappearances in their territory. Working together on this mystery could bring them closer.
Romance is also a common theme. Writers like to imagine a relationship between Ichigo and Halibel, which can be a really interesting take considering their different personalities and allegiances in the original story. It can range from a slow - burn relationship to a more sudden and passionate one.
In fanfiction, the idea of Ichigo and Halibel having a baby can lead to very interesting stories. It would combine the unique powers and personalities of both characters. For example, the baby could inherit Ichigo's Shinigami powers and Halibel's Arrancar abilities, creating a truly powerful and unique being. This concept could also explore how the two different worlds they come from, the Soul Society and Hueco Mundo, would react to such a union.
It could mean a new kind of power dynamic. The baby might have abilities that are unheard of, combining the Quincy, Shinigami, and Arrancar powers that are related to Ichigo and Halibel in some ways. This could change the balance in the fictional universe.
There's also 'Love in the Rukongai'. In this fanfiction, Ichigo and Halibel meet in the Rukongai and gradually develop feelings for each other. It's interesting because it shows a side of their relationship that we don't often see in the original series, with them learning about each other's pasts and growing closer.