In this fanfic, it could be that Ash is turned into Pikachu as a result of an experiment gone wrong. As Pikachu, he discovers new abilities and senses that he didn't know about before. He might form closer bonds with other Pikachu in the wild and learn their ways of living. He could also have to face challenges like being hunted by other Pokémon that see him as an easy target, and he has to use his new Pikachu - like skills to survive and try to find a way to turn back into his human form.
One possible plot could be that Ash starts his journey with a different starter Pokémon, like Bulbasaur. Without Pikachu by his side, he might face different challenges and form different relationships. He could struggle more in the early battles without Pikachu's electric power, but then develop unique strategies with his new Pokémon team.
Well, perhaps Ash starts to idolize Pikachu after seeing its unique powers in a battle. He might try to imitate Pikachu's moves and even start collecting Pikachu - themed items.
It could be a rogue Pokémon trainer who wants to capture Ash - now as Pikachu - for his own collection. This trainer might have a cruel streak and not care about the well - being of Pokémon.
In the 'Ash becomes a Pikachu fanfiction', Ash could have dreams where he is actually a Pikachu. This could lead to some really interesting adventures. For example, he wakes up in a dream as a Pikachu and has to figure out how to use his new form to battle. He might also make new Pikachu friends in his dream world and learn their unique ways of living. This could then have an impact on how he treats Pikachu in the real world when he wakes up, like being even more protective and affectionate towards his beloved Pikachu.
One possible plot could be that Ash turns into Pikachu and has to learn how to communicate with his human friends in this new form. He might struggle at first, but then discovers that he can use his Pikachu abilities in unique ways to help the group in battles and in solving problems around them.
Another idea could be a more emotional story. The female Pikachu gets separated from her group for some reason. Ash finds her and takes it upon himself to reunite her with her family. During this time, they have to endure harsh weather conditions and dangerous terrains. As they spend time together, they develop a deep connection that is based on mutual care and the shared goal of getting the female Pikachu back to her loved ones.
A plot twist could be that Ash's newfound 'Pikachu - fandom' causes a rift between him and his other Pokémon. They feel neglected because he is so focused on Pikachu. But then, through a series of events, Ash realizes that he needs to balance his love for Pikachu with his care for his other Pokémon friends. This realization could lead to a more harmonious relationship among all of them in the end.
Well, it could be about Ash waking up one day as a girl and having to deal with all the changes in his, now her, life. Maybe she has to adjust to new social dynamics, different reactions from friends and rivals, and also how to handle Pokémon battles in a different body.
Perhaps the story could involve Ash being transformed into a Pokémon through some magical or scientific experiment gone wrong. As a Pokémon, he would join a group of other Pokémon on a journey. He might face challenges like being hunted by Pokémon hunters or having to prove himself to a Pokémon tribe. Along the way, he'd also learn about the different perspectives of Pokémon in their own world.
The plot could be as simple as Ash training an Electrivire in secret. When Gary challenges Ash to a battle, Ash unleashes the Electrivire, which is much more powerful than Gary expected. Pikachu could also be involved by taunting Gary's Pokémon during the battle, adding to the overall scare factor.