One common theme is loyalty. Byakuya's loyalty to his family or those he considers family is often explored. Another theme is protection. He is often depicted as a protector in these fanfics.
Well, family bonds are a huge theme. These fanfics usually focus on how Byakuya's relationships with his siblings or family members shape him. Also, honor is a common theme. Byakuya is a character associated with honor, and fanfics often show how this affects his actions as a brother, like upholding the family name and values.
Another theme is the exploration of their powers in unique situations. For example, some fanfics might have them team up against a new and powerful enemy, and the story focuses on how they combine their abilities to fight. It can be really exciting to see how their different fighting styles work together.
One common theme is friendship. Despite their differences, they often form a deep bond in fanfics. For example, in many stories, they start off as rivals but gradually become friends who support each other.
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.
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.
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.
One common theme is the exploration of Byakuya's reserved nature. Since he is a very stoic character in the original series, fanfics often focus on how the reader can break through that exterior. For example, in many fics, the reader is shown to be the one who can make Byakuya show his more vulnerable side.
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.
Another theme is the idea of breaking boundaries. In the context of the Soul Society, there are rules and hierarchies. A fanfic might focus on how their relationship defies these, like Byakuya being from a noble family and Ichigo being a human - turned - Soul Reaper. It's about them crossing those lines for love.
One common theme is the exploration of an unlikely friendship. Given their different natures, it's interesting to see how they become friends. Another theme could be power dynamics. Byakuya is very powerful, and Orihime has her own special powers, so how they interact in terms of power is often explored. For example, how Byakuya protects Orihime or how Orihime's powers might surprise Byakuya.