He might meet some local Sinnoh trainers who are experts in training specific types of Pokémon, like a trainer who specializes in ice - type Pokémon in the colder regions of Sinnoh.
Ash might meet some lone Pokémon trainers. These trainers could be on their own quests, similar to Ash's. They might have unique Pokémon or training methods that Ash can learn from.
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 wise old hermit who lives in a secluded forest that Ash meets during his solo travels. This hermit might have a deep knowledge of Pokémon lore and give Ash some valuable advice.
Well, perhaps in this fanfiction, Ash is on a solo quest in Sinnoh to find a way to improve his Pokémon training skills even further. He could be traveling from one town to another, meeting new trainers who give him unique tips. Along the way, he might encounter some legendary Pokémon that test his abilities in unexpected ways. This would not only be a great adventure for Ash but also a chance for him to grow as a trainer without the help of his friends.
He might meet Serena again. Since he has been to Alola and now travels to Kalos, their reunion could be an interesting plot point.
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.
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.
He could make friends with Dawn. She's a well - known character in Sinnoh and her knowledge of Pokémon contests could be really helpful to Ash. Another potential friend could be Barry. His energetic and competitive nature would make for some interesting interactions with Ash.
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.
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.