Power dynamics is a common theme. Yujiro is often depicted as extremely powerful, and the relationship with the OC can be shaped by this. For example, the OC may be in awe of his strength or try to prove themselves equal to him.
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.
One possible plot could be a crossover where Yujiro Hanma somehow finds his way into the wizarding world of Harry Potter. Maybe he's on a quest for ultimate power and hears rumors of the powerful magic there. He could start challenging the most powerful wizards, like Dumbledore, thinking their magic is just another form of strength to be conquered.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works from various fandoms, including Yujiro Hanma fanfiction. Just use the search function and type in 'Yujiro Hanma' to see what's available.
A crossover with 'One Punch Man' would also be interesting. Yujiro Hanma might initially see Saitama as a weakling due to his unassuming appearance. But as the story unfolds, he realizes Saitama's true power. It could lead to some really comical and action - packed scenes as they interact.
If Naruto were to act like Yujiro in a fanfiction, it would change his relationships too. He would no longer be the overly - friendly Naruto we know. He might become more aloof and selective with his friendships. His interactions with Sasuke could be different. Instead of constantly trying to bring Sasuke back with kindness, he might use a more forceful and intimidating approach, just like Yujiro would deal with those who oppose him.