In a crossover with One Piece, Luffy could be an ally. Luffy is known for his open - mindedness and ability to befriend almost anyone. He would see Broly's power and might try to get him to join his crew or at least fight alongside him against common enemies. They could have some really fun interactions, like Luffy trying to make Broly laugh or share his love for food with him.
Issei could be one of Broly's potential friends. Issei is known for his friendly and outgoing nature. He might be intrigued by Broly's power and want to befriend him. Also, Asia could be a friend. She has a kind heart and might reach out to Broly, who could be seen as an outcast due to his strength and different background. Her kindness could break through to Broly.
Perhaps a Saiyan female. Since Broly is a Saiyan, it would make sense for him to be paired with someone from his own race. They could bond over their Saiyan heritage and power.
One common theme is friendship. Despite coming from different backgrounds, Naruto and Hanma often form a bond in these fanfictions. Another theme could be power - struggle, as they compare and combine their different powers.
One main theme is loyalty. Given their characters, the exploration of whether they are truly loyal to each other or have their own hidden agendas is often a key part. For example, in many fanfics, Kisaki's manipulative nature might put their loyalty to the test.
When writing a Harry Potter and Yujiro Hanma fanfiction, it's important to establish the rules of the combined world early on. Will Yujiro be able to use magic? If not, how will he defend himself against magical attacks? You can also play with the idea of cultural differences. Yujiro comes from a very different kind of world compared to the wizarding world. This can lead to some interesting misunderstandings and comical situations. For instance, Yujiro might think the Sorting Hat is some kind of strange creature trying to attack him and try to fight it off. As you write, keep the pacing right, not too slow or too fast, and make sure the story has a satisfying ending, whether it's a happy ending or a more bittersweet one.
One interesting Yujiro Hanma fanfiction could be about his early days of training. It might explore how he developed his extreme strength and fighting skills. Maybe it shows his encounters with various opponents during his youth and how he overcame them to become the fearsome fighter he is known as.
Bulma could be another character paired with the reborn Broly. She might be the one to help him understand the modern world if he is reborn in a different time period. She could use her intelligence to create devices that help Broly control his power better or she could just be there to provide some comic relief in the midst of all the intense Saiyan drama.
He could team up with Luffy. Luffy is always open to new allies, and Broly's power would be a great addition to the Straw Hat crew. They could go on adventures together and face powerful enemies.