He might go on adventures to find different Eevee evolutions. Since Eevee can evolve into many forms like Vaporeon, Jolteon, and Flareon, Ash could search for special stones or places that trigger these evolutions. He could also enter Eevee - only competitions in the fanfiction world.
Well, in this fanfiction, Ash as an Eevee could have some really unique adventures. Imagine he tries to communicate with other Eevee in ways he never thought possible before. He might learn about the secret languages or signals that Eevee use among themselves. And then there could be a journey where he has to find a special Eevee trainer who can help him master some new moves that are specific to Eevee. Along the way, he would meet different Pokemon species that react differently to an Eevee - Ash, which would add a whole new layer of complexity and fun to his adventures.
Percy might embark on an adventure to find other lost Greek demigods who have somehow ended up in Roman territory. With his memories, he'd be more aware of the signs and ways to track them down. He could also be on a mission to discover the secrets of the Roman gods that the Greeks don't know much about, in order to strengthen the relationship between the two pantheons. And he might get involved in a battle against some ancient monster that the Romans thought was long defeated but Percy knows is still a threat due to his past experiences.
In this fanfiction scenario, Ash and Charmander could have an adventure in a volcanic area. Since Charmander is a fire - type, it would feel right at home there. They might discover a new type of Pokemon that is only found in volcanic regions. Also, Ash could participate in a local fire - type Pokemon tournament in this area. With Charmander's growth and training, they could potentially win the tournament and gain some rare items or Pokemon eggs as rewards.
Ash might have trouble in areas with a lot of water or grass-type Pokemon. Training fire-types to handle different terrains and opponents would be part of his adventure. Plus, he might have to deal with rivals who have a better understanding of fire-type strategies.
He could have adventures exploring new regions in the Pokemon Horizons universe that haven't been shown in the main series. Maybe he discovers a hidden island full of rare and unique Pokemon.
Some fanfictions might show Ash becoming a sort of honorary Pokemon Ranger. He would then have to balance his duties as a Trainer and as a Ranger. This could create internal conflict for him as he tries to decide which role is more important at different times. His friends from the Pokemon journey, like Brock and Misty, could also be involved, adding more layers to the story.
His relationship with Pikachu would become quite different. Pikachu might have to take on a more protective role. Instead of Ash being the one in charge, Pikachu would be looking out for Eevee - Ash. They would still have a strong bond, but it would be based more on Pikachu's guardianship now.
Well, Ash and his Pokémon might get involved in local Alola festivals. His Pokémon could participate in Pokémon - themed contests or challenges during these festivals. Also, they might team up with local trainers and their Pokémon to protect Alola from any potential threats, like a group of wild Pokémon causing chaos in a village.
One great aspect of a fanfiction where Ash starts in Kalos is that the environment is so different from what he's used to. The Kalos region has its own set of challenges, like the mega - evolution phenomenon. Ash could get involved with researching about it early on. He might also form new friendships with characters like Serena right from the beginning, and together they could embark on a journey filled with new discoveries and exciting battles.
He could go on a journey to find more of his kind. Since he still has his powers, he'd be better equipped to face the challenges of outer space and any potential threats while searching for other members of his race.
He could face new Pok茅mon species and challenging gym battles. Maybe he'll also make unexpected friends and rivals.