He could meet Leon, the undefeated champion of Galar. Ash would surely be excited to battle such a strong trainer and learn from him.
Ash might encounter new Pokémon in Galar. For example, he could come across Grookey, Scorbunny or Sobble, the starter Pokémon of Galar. He may also meet new trainers and have exciting battles with them.
He could meet an experienced trainer who becomes his mentor. This mentor could teach Ash some advanced Pokémon training techniques that he hasn't known before.
Lillie is a likely character. She could befriend Ash and they might go on Pokémon adventures together. She has her own story and growth in the Alola region, and interacting with Ash could add more depth to both of their characters. Also, Ash might meet the Trial Captains like Mallow or Sophocles. They could challenge Ash in different ways and teach him about the island challenges.
Ash might meet a strict teacher who has no idea about Pokémon at first but gradually becomes interested in them. He could also meet a rival in school who challenges him not only in academics but also in Pokémon battles.
Ash is a well - known character in the Pokémon franchise. In Galar fanfiction, he might be famous for his unique Pokémon battles, his journey through the Galar region, and his interactions with other characters. Maybe he's famous for his ability to bond with different Pokémon species found only in Galar.
He might meet some of his old friends again, like Brock or Misty. Maybe they will join him on his new journey through the regions.
He might meet Gary again. They could have a friendly chat or even a Pokémon battle.
There might be other trainers in the Galar region who could be main characters as well. They could be Ash's new friends or rivals. For example, characters like Hop, who is Leon's younger brother, could play a significant role in the fanfic.
He could meet Serena, who might be his travel companion or a friendly rival. Also, Clemont and Bonnie are likely characters he'd encounter. They could help Ash with his journey in Kalos, like Clemont with his inventions and Bonnie with her cheerful nature.
It could be a powerful and jealous Galar trainer. This trainer might see Ash as a threat to their own reputation and success in the region. They would then use their influence and charm to turn Ash's friends against him.