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.
Definitely. The idea of Ash and Pikachu's friendship is very popular in fanfiction. Their relationship is iconic. Fanfictions could tell stories of how they first met and how that initial connection grew into an unbreakable bond. It could also include side characters from the Pokémon world who notice and are inspired by their friendship, like Misty or Brock seeing how Ash and Pikachu always have each other's backs.
One possible reason could be that Ash senses a dangerous situation where Pikachu's full power might attract unwanted attention or put them in more danger. For example, if there are powerful and unseen enemies nearby, Ash might hold Pikachu back to keep a low profile.
In a fanfiction, Ash and Pikachu could enter a Pokemon contest where the theme is lemons. Pikachu has to use its skills in a creative way related to lemons. Ash trains Pikachu hard, and they come up with a unique performance where Pikachu zaps lemons to create a spectacular light show. This earns them high marks from the judges and they make new friends among the other contestants.
He might meet Pikachu first. Since Pikachu is his closest and most loyal Pokemon friend, it would be likely that Pikachu would be by his side when he wakes up. Pikachu could be really confused at first but still show concern for Ash in his new state.
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.
There is no such official or acceptable fanfiction. Pikachu is a Pokémon and Ash is a human character, and such a concept goes against the nature of the Pokémon world and is also inappropriate and unethical.
Growth is also a theme. Ash is constantly growing as a Pokémon trainer, and in fanfictions, this growth can be depicted in different ways. Maybe he learns new training techniques with Pikachu's help, or he overcomes personal fears that were holding him back in his journey.
The fanfiction could start with Ash and Pikachu finding a magical lemon. When Pikachu touches it, it gets the ability to communicate with all lemon - related Pokemon. They meet a lemon - scented Jigglypuff that tells them about a hidden treasure in a lemon grove. Ash and Pikachu set off to find the treasure. Along the way, they face many challenges, like crossing a river of lemonade and fighting off other Pokemon who also want the treasure. In the end, they find the treasure which is a special lemon that can heal any Pokemon's wounds.
The original relationship is based on trust and Pikachu's eagerness to battle. In the 'ash holds back pikachu fanfiction', this changes as Ash is restricting Pikachu. This deviation can explore different aspects of their bond, such as how they communicate and resolve this new situation. It could show a more nuanced side of their relationship, with Ash having to make tough decisions regarding Pikachu's actions.