Harry is the central figure in this fanfiction. Since he finds the Pokemon egg, he'll be the one driving the story forward. However, other characters like Hagrid could also play a role. Hagrid loves all kinds of magical creatures, and a Pokemon egg would surely pique his interest. He might give Harry some advice on how to take care of the egg. Dumbledore could also be involved, as he always seems to know more than he lets on and could guide Harry in understanding this strange new entity.
Obviously, Harry would be the main character as the title says he's the one who finds the Pokemon egg. His friends Hermione and Ron would probably be important characters too. They are always by Harry's side in most of his adventures in the wizarding world, so it's likely they'll be involved in this strange new discovery as well. And, of course, the Pokemon that hatches from the egg would also be a key character.
Well, in a story like this, Harry might first be really surprised to find the Pokemon egg. He'd probably try to figure out what it is. Maybe he takes it to his friends, like Hermione and Ron, and they all start researching about it together. They could be confused because Pokemon eggs are not from their world. Then, as the story progresses, the egg might hatch and out comes a cute little Pokemon. Harry would then have to learn how to take care of it.
Obviously, Harry Potter would be one of the main characters. He is the one who finds the One Ring after all.
Obviously, Harry would be one of the main characters since it's in his name. His friends like Hermione and Ron would probably also be in it. They often accompany Harry on his adventures. And there could be some antagonists as well, maybe some dark wizards or magical creatures that try to stop Harry from finding his energy core.
Team Rocket would be the most obvious ones. They're always after rare and powerful Pokémon or Pokémon - related items, so the legendary egg would be a huge target for them.
It could be an Eevee. Eevee is a very common yet special Pokemon. It has the potential to evolve into many different forms, so it would be an interesting addition to Fem Ash's team.
He might meet an old Pokémon expert who gives him tips on hatching the egg.
He could meet some Pokemon trainers. They might come looking for the lost Pokemon egg and Naruto would have to decide whether to give it back or keep it.
His best friends Hermione and Ron would surely be there to help. Hermione with her vast knowledge of magic could research about the egg, and Ron with his loyalty would stand by Harry's side in any danger related to the egg.
Obviously, Ash would be the main character since he's the one collapsing. His Pikachu would most likely be a key character as well. Pikachu is always by Ash's side and would probably be very concerned and try to help when Ash collapses.
Obviously, Paul would be a central character, even though he's dead. His friends and rivals are likely to be main characters too. For instance, Ash, who has interacted with Paul multiple times, would probably play a significant role. His Pokemon could also be important characters in a way, as they are left without their trainer. Other trainers in the Pokemon world who knew Paul, like Dawn or Brock if they had a connection to him, might also be main characters as they deal with the aftermath of his death.