Well, it could start with Harry being mysteriously transported to Byakuya's world. Byakuya, seeing Harry as an interesting case, decides to take him in. Harry would then have to deal with the cultural shock. He might be exposed to new forms of magic or power systems. And as he grows up under Byakuya's tutelage, he could form new relationships with the people in Byakuya's world, and together they might face various challenges, both internal and external, that test their bonds and their growth as individuals.
Harry's character would likely become more stoic. Byakuya's influence would make him more reserved in showing emotions. He might also become more strategic in his thinking, as Byakuya is known for his calculated moves.
Byakuya might be a powerful wizard from a different magical culture who comes to Hogwarts to share knowledge or to seek something. He could play a role in the fight against Voldemort, bringing his own combat skills and strategic thinking to the table. He could also form relationships with the main characters, like Harry, Hermione, and Ron, and influence their development in different ways.
It would be really strange and interesting. Byakuya from Bleach is a very different character from those in Harry Potter. Maybe it would involve Byakuya suddenly finding himself in the wizarding world of Harry Potter. He would likely be confused at first by the magic that is so different from his own spiritual power in Bleach.
A plot could involve Byakuya being sent to the wizarding world on a mission. He meets Harry Potter, who is intrigued by this strange and powerful being. Harry shows Byakuya the wonders of magic, and Byakuya in turn shares his knowledge of the Soul Society. As they spend more time together, they find themselves drawn to each other. However, there are those in both worlds who see their relationship as a threat or an abomination. They have to fight against prejudice and also against an evil that wants to use their relationship for its own dark purposes.
One interesting fanfiction could be about Byakuya Kuchiki visiting Hogwarts. He might be intrigued by the magic there, which is different from his own spiritual powers. He could interact with Harry Potter and learn about the wizarding world's unique concepts like the Houses and the Forbidden Forest.
In a fanfiction, their interaction could be quite complex. Byakuya, with his noble and reserved nature, might be initially dismissive of Harry's more impulsive and emotional tendencies. But as they face challenges together, like a new threat that combines the dark magic of the wizarding world and the Hollows of the Soul Society, they would have to rely on each other's strengths. Harry's ability to think on his feet and his experience with various magical creatures could complement Byakuya's strategic mind and powerful combat skills.
One possible storyline could be a crossover where Harry Potter's magic world collides with Byakuya's world. Maybe Harry gets lost in Byakuya's realm and has to learn their ways to find his way back home. Another could be a team - up between them to face a common enemy that threatens both their worlds. They could combine their unique skills, Harry's magic and Byakuya's combat abilities.
Ron could also be there. He might be a bit jealous at first if Harry's adopted family is wealthier or has more influence in the wizarding world. But later, he would support Harry as always.
One common theme is family. Since Harry is being adopted, the new family dynamics, love, and acceptance are often explored. For example, how he forms bonds with his new family members.