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.
In a fanfiction about Ash born in 1987 and his situation in 1997, we could see an alternate story where Ash is not the typical rookie trainer. Since he's a bit older than in the original, he might be more knowledgeable about Pokémon lore. He could be on a quest to uncover some ancient Pokémon secrets in 1997. He might travel to different regions, not just for battles but also to study old Pokémon texts and artifacts, and along the way, form an unusual team of Pokémon that are attracted to his in - depth knowledge.
He might be initially shocked. Ash has always been surrounded by friends and supporters, so suddenly being betrayed by everyone would be a huge blow. He could be in disbelief for a while.
There could be unfinished business between them. They might have a shared goal that they haven't achieved yet. Greninja's return to Ash in the fanfiction could be to finally complete that goal, whether it's winning a particular Pokemon tournament or saving a certain place from destruction.
I'm not sure specifically what this particular 'ash pokemon ash alola blind fanfic' is about without reading it. It could potentially be a fan - created story where Ash is in the Alola region and has some sort of blindness - related plotline. It might involve his adventures in the Alola region with his Pokémon while dealing with this new handicap, like how it affects his battles or his relationships with other characters.
In general, Ash is often depicted as his adventurous and determined self. He might be shown as being a bit naive at times. Iris, on the other hand, is usually portrayed as strong - willed and feisty. However, it's important to note that spank fanfiction is not a typical or widely - accepted form of fanfiction and may contain elements that are not in line with the original characters' personalities in a more official sense.
Pikachu would be a likely candidate. Pikachu is Ash's most loyal Pokémon and has a very strong bond with him. It would sense that Ash is in trouble and would go on a mission to rescue him. Pikachu could use its electric attacks to fight off Gary or any obstacles in the way.
In some fanfictions, Ash can touch Pokémon to show a deeper bond. It might be a way for the author to create more emotional and physical interactions between Ash and his Pokémon pals, different from the normal anime where physical contact like hugs is not as common.