A common theme is the power dynamic between them. Byakuya is much more powerful and experienced than Rukia initially. Fanfics can explore how this gap changes over time as Rukia gets stronger. Additionally, the theme of forgiveness. Given their past misunderstandings and differences, fanfics often feature a plot where they have to forgive each other for past mistakes in order to move forward in their relationship.
Growth is a frequent theme. Rukia grows as a Soul Reaper under Byakuya's watch, and Byakuya himself may also experience personal growth through his relationship with Rukia. Fanfics might show how they help each other become better versions of themselves. Also, the theme of sacrifice. There could be situations where either Byakuya or Rukia has to sacrifice something for the other's well - being or for the greater good of the Soul Society.
One common theme is family. Even though they are not related by blood in the traditional sense, Byakuya has been like a family figure to Rukia. So, fanfics often explore this family - like bond and how it affects their decisions. Another theme is loyalty. Both are loyal to the Soul Society, but their loyalty to each other can sometimes be in conflict with the rules of the Soul Society. This creates interesting plotlines in fanfics.
One common theme is family. Since Byakuya is Rukia's adoptive brother in the Bleach universe, many fanfictions explore the complex family dynamics between them. It could be about Byakuya's over - protectiveness or Rukia's struggle to fit into the Kuchiki family.
One common theme is family loyalty. Despite the cold exterior that Byakuya often shows, his loyalty to Rukia as his sister is a central aspect. Another theme is sacrifice. In many of these fanfics, either Byakuya or Rukia is willing to sacrifice for the other's well - being.
One common theme is loyalty. Given their history in the original story, loyalty to each other, whether it's rukia's loyalty to byakuya as her superior or byakuya's loyalty to rukia as someone he cares about deeply, is often explored.
One common theme is loyalty. Byakuya's loyalty to his family, which includes Rukia, is often a driving force in these fics. Another theme is redemption. Byakuya might be redeeming himself for past actions or misunderstandings regarding Rukia.
One common theme is redemption. Byakuya may have things in his past that he feels he needs to make up for in relation to Rukia. Another theme is family. Since they are related in the Soul Society context, the idea of family and how it affects their relationship is often explored.
One common theme is loyalty. Byakuya is bound by his loyalty to the Soul Society and his family, and Rukia has her own sense of loyalty. Their relationship often has to navigate through these loyalties. For example, in many fanfics, Byakuya has to balance his duty to his family's name and his growing feelings for Rukia.
A very emotional one is 'Hisana's Legacy'. It shows how Byakuya still holds onto Hisana's memory and how that affects his relationship with Rukia. The pain and longing that Byakuya feels are palpable throughout the story.
Another common theme is regret. Hisana's regret for leaving her sister is often a central point. Fanfics might show how this regret affects her relationship with Byakuya or how Byakuya deals with her past.
One common theme is the exploration of their unspoken feelings. Since in the original series there's a certain tension between them, fanfictions often delve into what those feelings could be. Another theme is adventure, where they go on missions together and their relationship develops during those events.
One possible plot could be that rukia and byakuya accidentally end up taking care of a baby. They initially struggle as they are not used to this situation. Byakuya with his strict nature tries to impose order while rukia is more lenient. As they care for the baby together, they start to understand each other on a deeper level and their relationship grows stronger.