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.
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.
I'm not sure if there is a specific 'ash no pikachu fanfic' out there. There are countless fanfics in the Pokémon fandom, but this particular one might be hard to find. You could try searching on dedicated fanfic websites like FanFiction.net or Archive of Our Own and use the relevant keywords to see if it exists.
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.
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, 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.
In a fanfic, Ash might tell Gary a spooky story about an Electrivire that went berserk. With Pikachu by his side for added effect, Ash could describe in vivid detail how the Electrivire was uncontrollable and its power was overwhelming. Gary, being a competitive trainer, would be both scared and intrigued, wondering if he could ever handle such a Pokémon. This could play on Gary's insecurities as a trainer and create a great story of fear and rivalry.
I'm not sure if there is an exact 'ash x pikachu lemon fanfic' available. Fanfics can be quite diverse, but this combination seems rather strange as Pikachu is a Pokémon. Most Pokémon fanfics focus on more common relationships within the Pokémon universe, like trainer - Pokémon partnerships in a non - strange way.
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.