Voldemort is often involved. Since he's Harry's main enemy, he might set up elaborate plans to kill Harry. For instance, he could use a powerful artifact to lure Harry into a deadly situation.
There could also be the villains. Depending on the context of the fanfiction, it might be Dr. Eggman. He's always trying to cause trouble for Sonic and his friends, and he could be the one behind the situation where Tails almost dies. So Dr. Eggman would be a main character on the opposing side.
Annabeth is often the one to save Percy. She's smart and resourceful. For example, she might use her knowledge of architecture to find a way out of a collapsing building that Percy is trapped in. Or she could use her strategic thinking to outwit a monster that has Percy at its mercy.
Hermione is often involved. She might be the one helping Harry with the spells or potions to change his identity, like brewing the Polyjuice Potion correctly. Ron could also be involved, perhaps providing moral support or getting into trouble while trying to keep Harry's new identity a secret.
Ron could also be there. He might be in charge of something like the Gryffindor Quidditch team or be a part - time teacher teaching the younger students about the magical history of the Weasley family's inventions. His humor and loyalty would be a great addition to the story.
Obviously, Harry Potter himself is often a central character. His friends like Hermione Granger and Ron Weasley also frequently appear. In some fanfictions, they might play different roles compared to the original books. For example, Hermione could be the one who stumbles upon a dark secret first and has to convince Harry and Ron to take action.
In certain fanfictions, Jiraiya could be involved. He might be the one who discovers Naruto's potential to open the gates in a unique way. He could train Naruto further, teaching him how to combine the power from opening the gates with his other jutsu. Also, Hinata could be around, cheering Naruto on when he shows off his gate - opening skills during a battle or a training session.
Harry Potter himself is often involved. He might be the one to encounter the first signs of inflation, whether it's a magically inflating potion or an enchanted object. His friends, like Ron and Hermione, are also likely to be part of the story, helping him figure out what's going on.
Ron Weasley could also be a key figure. He might be Harry's loyal friend as always, standing by his side during all the changes that Harry is bringing about in the wizarding world as a god. And there could be new characters introduced as well, perhaps other gods or magical beings that interact with Harry in this new fanfiction realm.
In some cases, Albus Dumbledore could play an important role. His wisdom and power in the wizarding world would make him a key figure in any situation where the two different universes collide. He might be the one to first discover Alexstrasza's presence and figure out how to make use of her abilities in the fight against the dark forces in the Harry Potter world.
Obviously, Harry Potter himself is always a main character. He is the one most directly associated with the concept of death in the original series, what with his parents' death and his multiple near - death experiences.