A really cool Ash leaves Alola fanfiction could involve him leaving behind a special Pokémon in Alola for a particular reason. This Pokémon then becomes a sort of legend in Alola, and when Ash finally returns, he has to deal with the new status and role of his old Pokémon friend. The story could explore how Ash and the Pokémon reconnect and how the Alolan people now view this Pokémon differently.
One interesting Ash in Alola fanfiction could be about Ash training a new and rare Pokémon in Alola. For example, he might discover a hidden ability of a Pokémon native to Alola that no one else knew about.
Another great Alola Ash fanfiction idea is that Ash discovers a hidden part of Alola filled with ancient Pokémon. He teams up with his friends from Alola and they embark on an adventure to learn more about these Pokémon. Along the way, Ash learns new things about Pokémon history and how it relates to Alola.
You can try fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Ash leaves Alola' in their search bars, and you should get a list of relevant fanfictions.
A really cool fanfiction could be set in a post - apocalyptic world where ash covers everything and Pikachu is one of the few remaining Pokémon. Ash and Pikachu have to survive among the ash leaves, and they discover an ancient power within the Pikachu that is somehow related to the ash. This power could be the key to restoring the world or at least finding a new safe place to live.
One popular Ash Alola fanfiction could be about Ash having unique adventures in the Alola region that weren't shown in the original series. For example, he might discover a new type of Pokemon that only exists in a hidden part of Alola.
One interesting aspect is how Ash's intelligence changes his relationships. For example, in some fics, his smart decisions earn him the respect of more experienced trainers in Alola. This is different from the normal perception of Ash in the original series where he is more of a novice at times.
Perhaps in the 'ash in alola fanfic', Ash's growth as a trainer in the Alola environment is explored in depth. He might learn different training techniques specific to the Alola Pokémon.
One interesting Ash fanfiction could be about Ash having a special power in Alola that no one else has. For example, he might be able to communicate with all Pokemon without the need for a translator. This could lead to him solving many mysteries and helping Pokemon in unique ways.
One interesting storyline could be Ash forming a unique bond with a rare Alola Pokémon. Maybe he discovers a Pokémon that has special powers and they go on adventures together to help it control and understand those powers.
Another idea is that May decides to study Pokémon in Alola for a research project. Ash joins her to help. They visit different islands in Alola and encounter unique Pokémon training styles. They also face a group of poachers who are trying to steal some of the Alola Pokémon. Ash and May must use their skills and the help of their Pokémon friends to stop the poachers and protect the Alola Pokémon.