Yes, there are quite a few. You can start by searching on fanfic platforms like Fanfiction.net or Archive of Our Own. Some might explore unique crossovers between the 'Bleach' universe (where Hisana and Byakuya are from) and the 'Harry Potter' world, perhaps with magical elements from both being combined in interesting ways.
A plot could involve Hisana having some sort of special connection to the magic in the Harry Potter world. For example, she discovers she has a latent ability that is unique to that world. Byakuya, being protective of her, tries to keep her safe while also learning about this new magic. They might get caught up in Hogwarts politics or help the students there in some way. It could also explore how their relationship changes in this new and strange environment.
There is a fanfic named 'The Unspoken Ties'. In this, it focuses on Rukia's growth and how her connection to Byakuya and the memory of Hisana play important roles. It's a really engaging read as it explores the emotional depth between them. Rukia's journey of self - discovery while dealing with her past and present relationships is well - portrayed.
Love is a very common theme. Their love story, which was complex and filled with sacrifice, is often explored in more depth. Another theme is loss. Since Hisana is no longer alive in the main Bleach storyline, fanfics often deal with Byakuya's sense of loss and how he copes with it.
The theme of memory also comes up often. Fanfics might explore how Byakuya holds onto his memories of Hisana, how those memories shape his actions and decisions in the Bleach story. It could be things like his strictness in following the rules being related to his promise to Hisana, or his moments of softness being triggered by a memory of her.
Perhaps the fanfic could explore how the pregnancy affects Hisana's relationship with other characters in the Bleach universe. Maybe there are those who are overjoyed and those who are jealous or concerned. It could also involve some sort of danger or threat to the pregnancy, and how they overcome it.
A good 'Bleach' Hisana x Byakuya fanfic should first and foremost have well - developed characters. It needs to capture Hisana's gentle and selfless nature as well as Byakuya's stoic yet passionate side. For example, it could show Hisana's sacrifice for her sister in a way that makes the reader truly understand her character. Secondly, the relationship development is crucial. It should gradually build up their love, perhaps starting from a chance encounter to a deep, unbreakable bond. Like in the series, Byakuya's slow realization of his feelings for Hisana can be beautifully portrayed.
There's a fanfic called 'Byakuya and Hisana: Unspoken Love'. It beautifully portrays the unsaid emotions between them. It starts with Byakuya's memories of Hisana and then goes on to show how those memories affect his present actions. A lot of it is about his internal struggle with his feelings for her.
Love is a very common theme. Since their relationship was based on deep love, fanfictions often explore different aspects of their love, like how it started and how it endured. Another common theme is sacrifice. Hisana sacrificed a lot, and this is often explored in the fanfictions. For example, how her sacrifice affected Byakuya.
Byakuya and Hisana's love was a deep and complex one. Hisana was a gentle soul. Byakuya was drawn to her kindness. They shared many tender moments together, their love growing gradually. But unfortunately, Hisana's early death left Byakuya with a great sense of loss and longing that stayed with him for a long time.