One great story could be where the OC is a strong - willed martial artist who challenges Yujiro Hanma. Their interactions are filled with intense battles and mutual respect that gradually turns into a complex relationship.
First, understand the character of Yujiro Hanma. Know his personality traits like his extreme strength and pride. Then, create your OC with a distinct personality. Start with an interesting encounter between them, like a chance meeting at a fighting tournament.
The best way to know where to start is to look for discussions on manga-focused websites. Fans often share their experiences and advice on continuing after the anime. Another option is to check social media groups dedicated to Baki Hanma to get suggestions from fellow fans.
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.
Naruto's character would likely become more aggressive. Yujiro is a very aggressive character, and Naruto might start to show similar traits. He could be quicker to anger and more assertive in his actions.
I think Warhammer 40k fanfics are a great way for fans to explore the vast and complex universe further. A good fanfic can add depth to the existing lore. For example, it might focus on the daily lives of the Imperial Guardsmen, which we don't often get to see in the official works. But there are also those that are just not up to par. Maybe they lack proper grammar or have a really convoluted plot that doesn't make sense in the context of the 40k universe.