A new professor might be introduced. This professor could be an expert in a specific type of Pokemon or a new area of Pokemon research. For example, they might study the relationship between Pokemon and the environment in a more in - depth way than previous professors.
There could be a new rival for Ash. This rival might have a very different approach to Pokemon training, like focusing more on the beauty and grace of Pokemon rather than just battle strength.
There could be a lone traveler who Ash meets while he is alone. This traveler might have a unique way of training Pokemon that Ash has never seen before and could teach him some new tricks.
There could be a new trainer who has a very different style of training Pokémon compared to Ash. Maybe a young girl who uses music to communicate with her Pokémon. Another potential character could be an old Pokémon sage who has a vast knowledge of ancient Pokémon lore and can offer Ash some valuable advice on his journey.
Potential characters might include a new group of Pokémon thieves that Ash has to deal with. Also, there could be a local Pokémon healer who becomes an important part of the story. There might be some young Pokémon enthusiasts who look up to Ash and join him on his adventures. Another possibility is a reclusive Pokémon trainer who has some rare Pokémon and Ash tries to learn from them.
There could be a female trainer who becomes Ash's rival while he's disguised as a girl. She might be initially dismissive of him, thinking he's just another girl trying to make it in the Pokemon world, but later be surprised when she discovers his true identity.
There might be a young and inexperienced trainer who is lost. Ash, being the more experienced one, decides to help the trainer find their way. This new character could look up to Ash and in the process, Ash learns more about himself as a role model. It would be an interesting dynamic as Ash is usually the one being guided by his friends.
There could be a female mentor who takes Ash under her wing because she sees potential in her as a girl in a male - dominated world. This mentor could teach her unique skills and ways of dealing with Pokémon. Another potential new character could be a rival who is also a girl and has a different view on how to compete in the Pokémon world compared to Ash. They could have some interesting battles and exchanges of ideas.
There could be a new trainer who becomes Ash's rival. This rival might have a completely different training style, like focusing on Pokémon's special abilities rather than just their strength.
A mysterious Pokémon whisperer might appear. This character could have the ability to communicate with Pokémon in a unique way and help Ash better understand his Pokémon, which in turn helps him grow as a trainer during his time without his friends.
He could bring some Johto Pokémon like Houndoom. Houndoom is a Dark - type Pokémon that would add a new element to Alola's Pokémon diversity. Its intimidating presence and strong battle capabilities would surely make it a popular addition among trainers in Alola.
Another cool new partner for Ash in fanfiction could be Riolu. Riolu is strong and has the ability to sense auras. It could learn a lot from Ash and Pikachu and grow into a powerful Lucario. This would give Ash a Pokémon with great combat skills and a unique ability that could help in battles and in understanding other Pokémon's emotions.