Probably his friends from his adventures could show up. For example, Pikachu might be there as his constant companion. And maybe some of his human friends from the Pokémon world could be transferred to the high school setting, like Misty or Brock.
His teachers would be likely characters. They could be strict or kind, guiding Ash through his high school journey. Also, there might be bullies. Every high school has some, and they could add conflict to the story by picking on Ash or his friends.
There could be new characters created specifically for the high school fanfiction. These could be classmates with different personalities, like the nerdy kid who helps Ash with his studies, or the popular girl who Ash has a crush on. And don't forget the school principal who might have some interesting rules for Ash to follow.
One possible main character could be Misty. She could be a student at Harem High School who has a long - standing friendship with Ash. Her feisty and determined personality would add a lot of drama and interaction to the story. She might be jealous of the attention Ash gets from other students, creating some interesting relationship dynamics.
Obviously, Ash himself. And his Kalos friends like Serena would probably be there. Clemont and Bonnie might also make an appearance as they were important parts of Ash's Kalos journey.
Lillie is really interesting. She starts off as a shy girl but grows a lot in her confidence when it comes to Pokemon. Her relationship with her family and their connection to the Aether Foundation adds depth to her character. Then there's Kiawe, who is very proud of his Alola heritage and his strong fire - type Pokemon. His no - nonsense attitude and his eagerness to prove himself make him stand out. And Sophocles, the tech - savvy kid, is always coming up with cool gadgets to help in Pokemon battles or exploration, which is super fun.
Some fanfictions might have Misty betray Ash. Perhaps she gets lured by the promise of power or some valuable reward. She could be tricked into believing that Ash is no longer the friend she thought he was and that betraying him is for the greater good.
The OC themselves are often popular characters. Since they are original creations, they can have all sorts of unique personalities, abilities, and backstories. For example, an OC could be a shy but brilliant Pokemon trainer who gradually overcomes their insecurities with Ash's help.
Brock could also be a main character. Since he has knowledge about Pokémon care and breeding, he could be Ash's colleague in the fanfiction. They could work together on projects related to Pokémon health and nutrition.
Pikachu would most likely be there. Since Pikachu is Ash's closest companion, it would be involved in any story related to Ash. Maybe Pikachu could also have some sort of interaction with Mew, like being a bit jealous at first of Ash's new connection with Mew.
Yes, in Ash Champion of Orre fanfiction, there are likely other memorable characters. There might be a local Pokémon ranger who helps Ash navigate the dangerous parts of Orre. This ranger could have a deep connection with the local Pokémon and know their secrets. A female trainer who is known for her beauty and strength could also be a part of the story. She might initially be a bit of a mystery to Ash but later becomes an important ally. And don't forget about the local Pokémon breeders who might introduce Ash to new Pokémon breeding techniques specific to Orre.
Gary Oak is a likely character. He has always been a rival to Ash and in fanfiction, he might betray Ash out of jealousy or a desire to be the ultimate Pokémon trainer. Another could be Misty. Maybe she gets influenced by some external force or her own insecurities and turns against Ash. Brock could also be a candidate in some stories. If he falls in love with a girl who has a vendetta against Ash, he might be forced to choose between his loyalty to Ash and his new love interest.
Gary could also be important. Maybe in this fanfiction, Gary is a rival that Ash has to outwit and defeat in a more intense way compared to the original story. Their rivalry could be a major driving force for Ash's growth and success in the league.