One idea is that Ash enters a hidden tournament where the rules are different. To compete, he has to endure intense physical training, which gradually makes him muscular. Another could be that a powerful Pokemon's aura has an impact on Ash's body, causing him to become more muscular as he spends time with it.
One possible fanfiction could be about Ash training really hard in a special region where he discovers a new type of Pokemon that has a unique energy. This energy somehow affects his physical development, making him muscular. He then uses his newfound strength to overcome tougher challenges in battles.
Ash could be a Pokémon trainer with a different starting point in this fanfiction. Born in 1987, by 1997 he might have already made a name for himself in local Pokémon battles. He could have a team of Pokémon that he rescued from difficult situations, like a Charmander that was abandoned by its trainer. His story could revolve around giving these Pokémon a second chance and proving that Pokémon don't need to be 'perfect' to be strong.
One idea could be a fanfiction where a girl joins Ash on his journey. She might have a unique Pokemon that helps Ash in a difficult battle. For example, she could have a psychic - type Pokemon that can sense the opponents' next moves and help Ash strategize better.
In some fanfictions, the girl's clothes are related to her Pokemon evolution journey. Maybe when her starter Pokemon evolves, she gets a new set of clothes that symbolizes their growth together. It could be a more elaborate and powerful - looking outfit. Also, there are often stories where she dresses up to impress Ash or to show her confidence during a difficult battle. This could involve a flashy, battle - ready costume with bright colors and strong - looking boots.
One interesting idea could be Ash having unique hybrid Pokemon companions. For example, a Pikachu with some other type's features. Another could be Ash himself having some hybrid abilities, like being able to communicate with Pokemon in a new and enhanced way.
One idea could be that Ash discovers a new type of Pokemon that has unique abilities and is the key to solving a big mystery in the Pokemon world. For example, it might be able to communicate with humans in a way no other Pokemon can, and Ash has to learn how to work with it to stop an evil organization from using this Pokemon's power for bad.
One idea could be to explore Ash's first encounter with Pikachu from Pikachu's perspective. Maybe Pikachu was initially scared of Ash but then grew to trust him over time. Another idea is to write about Ash's first gym battle in a more detailed and dramatic way, like adding some internal thoughts of Ash during the battle.
One possibility could be that Ash disguises himself as a new trainer to enter a restricted Pokémon tournament. He might do this to prove that it's not just about the name or reputation of a trainer but the skills. He could use his Pikachu secretly and still show his amazing bond with Pokémon without being recognized.
In a fanfiction about Ash's reunion in Alola, perhaps he comes back to help with an ecological problem. The Alola region's unique ecosystem is in danger, and his friends call him for his expertise. Ash brings along some of his other Pokemon from his travels, and together they work to save the day while also having a great time catching up.
Another possibility is Ash becoming Lugia. Lugia is known as the guardian of the seas. As Lugia, Ash could explore the deep oceans, discover new species of Pokemon, and safeguard the marine ecosystem. He could use his psychic and flying abilities to interact with both water - and flying - type Pokemon, bringing a new era of harmony between different Pokemon types.