Ash could develop his character in Sinnoh by becoming more strategic in his battles. Since Sinnoh has a variety of strong and unique Pokemon, he'd need to think more carefully. Misty could develop by becoming more independent. Maybe she takes on some solo adventures in Sinnoh, away from Ash for a bit, and this helps her grow as a trainer.
In a fanfic about Pokemon working in Sinnoh with skill, trainers could play a crucial role. They might train their Pokemon to perform specialized tasks. The story could revolve around a trainer who discovers new ways to utilize their Pokemon's skills in Sinnoh. Maybe a Pikachu using its electric skills to power up machinery in an old mine in Sinnoh.
Well, in a fanfic, a Pokemon like Bulbasaur could use its grass - type skills to help with gardening in Sinnoh. It could plant and grow all kinds of beautiful flowers and useful plants.
Froakie is quite memorable. Its evolution line into Greninja has a cool and ninja - like aesthetic. In a fanfiction, it could be the trusty partner of the main character, using its speed and unique moves to get out of tricky situations. Another one is Sylveon. It's so cute and fairy - type, which adds a new element to the Kalos region. It could be used as a symbol of kindness and friendship in a story.
Ash may develop his skills further in Sinnoh fanfictions. He could become more strategic in battles, learning from the different types of Pokémon and trainers in Sinnoh. May, on the other hand, might expand her knowledge of Pokémon contests, incorporating Sinnoh - style elements into her performances. Their experiences in Sinnoh help them grow both individually and as friends.
In some fanfictions, Ash and May might get involved in a mystery in Sinnoh. For example, strange events are occurring that are affecting Pokémon behavior. They work together to solve the mystery, with Ash using his battle skills and May her knowledge of Pokémon contests. As they dig deeper, they find that an ancient power from Sinnoh's past is being misused.
Perhaps there is a threat to Sinnoh that only Ash's old Pokémon can help solve. Some kind of ancient evil that has knowledge of Ash's past Pokémon battles. Ash and his old Pokémon then have to work together to defeat this threat. They might need to combine their old strategies with new ones they learn in Sinnoh to succeed. And along the way, Ash might meet some of his old friends who are also in Sinnoh and they help him in his mission.
One plot idea could be Ash and Misty getting separated from their group in Sinnoh and having to rely on each other to survive in a strange, new area. They could encounter a rare and powerful Pokemon that neither of them has seen before. Another idea is that they discover an ancient mystery in Sinnoh related to a type of Pokemon evolution that was thought to be lost. This could lead them on a journey to uncover the truth and help a particular Pokemon evolve in a new way.
A young trainer from an underdog region who rises to be a leader in the war effort. He or she could have a unique bond with a Pokemon that gives them an edge in battles.
Professor Kukui is another common character. He serves as a guide and mentor to Ash in the Alola region. He might provide Ash with new Pokémon knowledge, especially about the unique Alola Pokémon species. And of course, there are the various Pokémon trainers that Ash meets and battles in the Alola region. These trainers can range from novice trainers just starting out to more experienced ones who pose a real challenge to Ash.