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.
The 'Dragon Ball Super Broly Novel' is an interesting expansion of the Dragon Ball universe. It delves deeper into the character of Broly, his backstory, and his power. It also explores the relationships between the other main characters in the face of this new and extremely powerful adversary. The novel may include more detailed descriptions of the battles, which are always a highlight in the Dragon Ball series.
One possible fanfiction could be about Cheelai's backstory. Maybe she was once a normal Saiyan on Planet Vegeta but was part of a lower - class family. She had to fight hard from a young age to survive. In the fanfiction, it could explore how her experiences on her home planet shaped her into the tough character we see in 'Dragon Ball Super Broly'.
A simple fanfiction idea could be that Broly and Cheelai start training together to become even stronger. They aim to be the top protectors in their part of the universe.
A very popular trope is the discovery of hidden powers. In Dragonball Super fanfiction, it might be a human character suddenly realizing they have Saiyan blood. In Harry Potter fanfiction, it could be a student finding out they have a special kind of magic no one knew about. The training montage trope is also seen often. If Harry Potter were to train with Goku, there would be a sequence of him getting stronger. In the Dragonball Super world, a wizard could have a training montage to master ki - based attacks. And of course, the 'enemies - to - friends' trope is popular. A Death Eater could become friends with a villain from Dragonball Super and then turn good.
One way to combine them creatively is through a crossover story. For example, imagine if Goku was transported to the wizarding world. He could use his Saiyan powers in magical battles. His super strength and speed would be a huge asset. Maybe he'd have to learn magic too, and his determination to master new skills would be an interesting plot point. Another idea could be having Harry Potter use the Dragon Balls. He might wish for something to defeat Voldemort, like the power to be immune to the Killing Curse. This kind of combination allows for new and exciting storylines that appeal to fans of both franchises.