One possible plot could be that Pikachu is exposed to a rare type of thunderstone during a powerful thunderstorm. This thunderstone has been charged with an ancient energy. Pikachu absorbs this energy and begins to evolve. But instead of evolving into Raichu right away, it goes through a series of strange and new intermediate forms, each with unique powers. As it evolves, Pikachu has to learn to control these new powers while also facing challenges from other Pokemon who are either jealous or see it as a threat.
A plot could involve Pikachu's bond with its trainer. The trainer discovers a mysterious item that is said to enhance a Pokemon's evolution. When Pikachu comes into contact with this item, it starts to evolve. However, the evolution process is not smooth. It has to overcome internal struggles related to leaving behind its old form and the identity it had as Pikachu. Along the way, Pikachu meets other evolved Pokemon who help it understand the process and the new responsibilities that come with being a more powerful and evolved Pokemon.
One possible plot could be that Pikachu is exposed to a rare form of electric energy in a thunderstorm that's charged with some mysterious power. This could start the evolution process. It might struggle at first, not understanding the changes its body is going through. As it evolves, it could gain new abilities like enhanced speed and a more powerful electric attack. And it might have to face new challenges in battles, as opponents are now more cautious of it.
A group of Team Rocket - like villains could be the main antagonists. They might want to capture Pikachu while it's in the process of evolving because they believe that an evolving Pikachu would have some special power that they could use for their evil plans. They constantly try to disrupt Pikachu's evolution and the bond between Pikachu and its trainer.
Another possibility is a rival trainer who has a Pokemon that is weak against Raichu. This trainer might try to prevent Pikachu from evolving to keep their own Pokemon's advantage in battles. They could try to steal Pikachu's food or training resources to slow down its growth and evolution.
The fanfic could be about Pikachu getting angry when a new powerful Pokemon arrives in the area and starts bullying the other Pokemon. Pikachu, being the brave little Pokemon it is, stands up to the bully. At first, it loses battles due to its anger getting the best of it. But with the support of its friends, it manages to channel its anger into strength and defeats the bully.
One possible plot twist could be that Bayleef suddenly loses its ability to use grass - type moves. This would put both it and Pikachu in a difficult situation as they rely on Bayleef's moves in battles. They would then have to find a way to regain Bayleef's power, perhaps by going on a quest to find a special herb or meet a certain Pokemon that can help.
A possible plot could be that Pikachu gets lost in a new forest. There, he meets a Sylveon. Sylveon helps Pikachu find his way back home. During their journey, Pikachu starts to develop feelings for Sylveon. Sylveon is also attracted to Pikachu's brave and friendly nature. When they finally reach Pikachu's home, they don't want to be apart and decide to stay together, facing any challenges that come their way as a couple.
One possible plot could be that Mimikyu is jealous of Pikachu's popularity. However, instead of becoming enemies, they end up in a situation where they have to rely on each other. For example, they get lost in a strange part of the Pokemon world. Through this experience, Mimikyu realizes that popularity isn't everything and Pikachu learns to see Mimikyu's true value.
One possible plot could be Pikachu getting influenced by a dark and powerful Pokemon. For example, a Darkrai might use its nightmare - inducing powers on Pikachu. This could make Pikachu start to attack other Pokemon and trainers without mercy. Maybe Pikachu would first target its own trainer, Ash, as it would be the most shocking turn of events. This would create a lot of chaos in the Pokemon world and force Ash and his other Pokemon friends to try and figure out how to save Pikachu from this evil state.
Well, it could be a story of rivalry at first. Pikachu is quite popular among trainers and other Pokemon, while Mimikyu is often overlooked or feared. Mimikyu might envy Pikachu's status and decide to challenge it to battles. But during these battles, they start to understand each other better. Pikachu realizes that Mimikyu is just lonely and wants some attention. So instead of fighting, they end up working together to help other Pokemon in need. For example, they might save a group of Pichu from a landslide by using their combined electric powers.
One possible plot twist could be that Pikachu suddenly loses its ability to use electric attacks. This would completely change the dynamic of the battle as Pikachu would have to rely on physical attacks like Quick Attack, which might not be as effective against Bayleef. Another twist could be that Bayleef evolves during the battle into Meganium, gaining new and more powerful abilities that catch Pikachu off - guard.