Well, it might involve Harry having some new powers related to Anubis. Maybe he can control certain death - related magic. For example, he could have the ability to communicate with the dead in a different way than the normal wizarding world allows.
Obviously, Harry Potter himself would be a main character. Since he's the son of Anubis in this fanfiction, he'll be at the center of the story. His friends like Ron and Hermione are also likely to be main characters. They would probably be involved in helping Harry understand and control his new powers related to Anubis.
In a 'Harry Potter meets Anubis' fanfiction, their power levels would depend on the context. Harry is a very talented wizard, but Anubis is a deity. However, Harry has defeated Voldemort, which shows his great power. If they were to face off, Harry might be able to hold his own for a while using his quick thinking and magical skills. But Anubis' power is more fundamental, related to life and death itself. So overall, Anubis would probably be more powerful, but Harry could surprise him with his resourcefulness.
Yes, there are likely to be such fanfictions out there. Fanfiction is a vast and diverse world, and it's common for fans to create crossovers between different fictional universes like 'Harry Potter' and the world related to Anubis. You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own to find them.
The relationships in the story would be different. His friends like Ron and Hermione would have to adjust to his new powers and status. They might feel a bit inferior at first, but Harry would likely assure them that they are still important. The wizarding families would also react differently. Some might see Harry as a threat to the traditional wizarding order, while others would see him as a potential savior with his new powers from being a demigod son of Anubis.
The story could involve Harry using Anubis - related magic. Since Anubis is associated with mummification, Harry might be able to use spells that turn his enemies into mummies for a short time. Also, his connection to Anubis could give him an enhanced sense of justice, which would play out in his fight against the dark forces in the wizarding world. He may also discover ancient Egyptian spells that are more powerful than the normal wizarding spells he knows.
He would probably be more in tune with death and the afterlife. Since Anubis is associated with death in Egyptian mythology, Harry might have a more solemn and respectful attitude towards it. He could also be more mysterious, as his connection to Anubis would set him apart from other wizards.
The plot could involve Harry being a reincarnation of Anubis. He might start to have strange dreams and visions related to his past life as the Egyptian god. As he tries to understand these, he discovers that his powers as Anubis are starting to surface. This could lead to him having to protect the wizarding world from a new kind of threat that only his combined powers can defeat.
He could be a powerful antagonist. Since Anubis is associated with death in Egyptian mythology, he might be interested in the power of the Deathly Hallows. He could try to steal them from Harry, believing they would give him more control over death in the wizarding world.
Identity is also a big theme. Characters in the fanfictions may struggle with their own identities when faced with the influence of Anubis. For instance, a character might question their place in the wizarding world if they start to have a connection with Anubis - related elements, or they might have to hide this new aspect of themselves from others.