One possible theme could be power struggle. Naruto and Black Adam both possess great power, and a fanfiction could explore how they deal with each other's power levels. Another theme might be friendship or rivalry. They could start as rivals but then develop a mutual respect.
Perhaps the plot could start with Naruto being an outcast not just because of the nine - tailed fox, but also because of his strange powers that he doesn't understand. Then, he has a vision or encounter that reveals he is the son of Black Adam. He then embarks on a journey to find out more about his father's world. Along the way, he meets new allies and enemies. His friends like Sasuke and Sakura might be initially suspicious of his new powers, but as they see him use them for good, they come to accept him. The fanfiction could end with Naruto using his combined powers to save both the ninja world and somehow be involved in a conflict in Black Adam's world as well.
Well, one possible plot could be that Naruto somehow gets transported to the DC universe and becomes a huge fan of Black Adam. He might see Black Adam's power and determination and be inspired to learn new jutsu or ways of fighting. Maybe he tries to incorporate some of Black Adam's battle tactics into his own style in the ninja world.
Well, I haven't read a specific 'naruto x black adam fanfiction' myself. But generally, when looking for such a crossover, you should consider the plot. It could be about a battle between them at first, and then they team up to face a greater threat. Maybe Naruto's chakra and Black Adam's magic could combine in some way in the story.
One possible plot could be Naruto discovers Black Adam's story through some kind of inter - dimensional rift. He is inspired by Black Adam's strength and sense of justice. So he tries to incorporate some of Black Adam's fighting styles into his own jutsu. He might also face some opposition from his friends who don't understand his newfound fascination with this strange hero from another world.
If Naruto were a Black Adam fan in a fanfic, Naruto would probably be in awe when he first meets Black Adam. He might stutter a bit while trying to introduce himself and ask a million questions about Black Adam's powers. Black Adam, on the other hand, might be a bit confused by Naruto's bright orange jumpsuit and strange hair, but would be intrigued by his enthusiasm.
There might be some very niche 'Naruto is the son of Black Adam' fanfiction out there. However, I haven't come across it myself. If it does exist, it could involve Naruto having some of Black Adam's powers like super strength and flight, which would completely change the dynamics of the Naruto universe. Maybe in this fanfiction, Naruto would also inherit Black Adam's sense of justice or his more anti - hero traits and have to navigate the complex world of ninjas with these new aspects of his character.