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.
Perhaps Ash has noticed that Pikachu is not in its best condition, like being a bit tired or injured. In that case, he would hold Pikachu back to prevent it from overexerting itself and getting more hurt. This shows Ash's care for Pikachu's well - being.
Another reason might be related to Pikachu's own growth. As Pikachu becomes more powerful and self - aware, it might feel that it needs to go on its own journey without Ash. It could be seeking new challenges and experiences that it believes Ash can't provide, like exploring regions that Ash has no intention of going to or training with Pokémon of a different caliber.
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.
Perhaps Pikachu is lured away by something more appealing. There could be a rare and powerful Pokémon or a special kind of food that distracts Pikachu from protecting Ash. Also, Pikachu might have received some false information. For example, it might have been tricked into thinking that Ash has a better chance of escaping the Spearow without it. In the heat of the moment, Pikachu makes a hasty decision based on this wrong information.
Maybe the creator wants to explore a different side of Pikachu's character. In the official story, Pikachu is loyal and friendly, but in this fanfiction, it could be a way to show a corrupted or influenced Pikachu. Also, it could be a way to deconstruct the typical hero - sidekick dynamic between Ash and Pikachu and make readers think about their relationship in a new way.
It could mean that Ash is somehow preventing or restraining the creation or spread of fanfiction. Maybe Ash has some kind of power or influence in the context where the fanfic exists, like in a particular fandom community, and is using it to hold back the development of fan - created stories.
If Ash is in a position of power in a fandom, they could hold back fanfic that they perceive as low - quality or not in line with the 'spirit' of the original. They might want to maintain a certain standard for the fan - created works. Maybe they think some fanfics are too self - indulgent or don't contribute positively to the overall fandom experience.
Perhaps Naruto is waiting for the right moment. He could be observing his classmates and the teachers in the academy to figure out who he can really trust. By holding back his power, he can better assess the situation and the people around him without revealing his full capabilities too soon. Also, he might not want to disrupt the normal order of the academy. Naruto might have a sense that if he goes all - out, it could cause chaos and that's not what he wants at this stage.
Well, in this fanfiction, if Ash turns into Pikachu, it might lead to a story where Pikachu - Ash discovers new aspects of the Pokémon world. For example, he could experience the world from a Pokémon's perspective, understanding their fears and joys more deeply. He might also have to deal with other Pokémon who don't immediately recognize him as Ash and react in different ways to this strange Pikachu.
One reason could be power. Maybe he was offered a great deal of power by an outside force in exchange for betraying the harem. Another could be jealousy. If there was someone in the harem who was getting more attention or was more successful than him in some way, he might have been driven by envy to betray them.
One reason could be a power struggle. If there was a rare and powerful Pokémon at stake, Ash might be tempted to betray Korrina to get it for himself. In the Pokémon world, power and rare Pokémon are highly coveted.