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.
There's also 'The Unlikely Alliance'. In this fanfic, Kisaki and Hanma find themselves in a situation where they have to work together against a common enemy. It shows a different side of their relationship, with some interesting plot twists.
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.
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.
A crossover with 'One Punch Man' would also be cool. Saitama's nonchalant power compared to Baki's intense training and determination could create an interesting dynamic. Maybe Baki tries to figure out Saitama's secret to his strength.