Some fanfictions might show a heroic sacrifice. For instance, Ash and Pikachu could be saving the Pokémon world from a great evil and in the process, lose their lives. Others may depict it as a sudden and unexpected event, like an illness or an accident. There could also be fanfictions where their deaths are a result of a long - drawn - out battle against a powerful foe that they ultimately can't win.
One common theme could be the sense of loss and grief among the other Pokémon and Ash's friends. For example, Pikachu was Ash's closest companion, so his death would leave a huge void. Another theme might be the exploration of mortality in the Pokémon world. It could also lead to a story about how the remaining characters grow and change in the face of such a tragic event.
It could be a new, young Pokemon who befriends the old Pikachu. This young Pokemon could witness Pikachu's decline and death, and through this experience, learn about the history and importance of Pikachu in the Pokemon world.
The fanfiction could be about how the Pokemon world has changed over time and Pikachu is left behind as an 'old - fashioned' Pokemon. It might face discrimination or neglect because of its age. The death of Pikachu could be a symbol of the end of an era in the Pokemon world. It could also explore how the younger generation of Pokemon and trainers view Pikachu's legacy.
The change in its appearance can make it scary. For example, if its usually cute yellow fur turns dark or if its bright red cheeks become a sinister red glow. Also, if it starts to behave in an uncharacteristic way, like making menacing noises instead of its usual cute sounds.
Obviously, the main characters are usually Pikachu. But sometimes, there could be other Pokémon that play important supporting roles. For instance, a Pichu could be a sidekick or a younger Pokémon that the Pikachus are protecting.
One interesting plot could be two Pikachus from different regions meeting and learning about each other's unique electric attacks. For example, one Pikachu might know a special move that the other has never seen before. They could then teach each other and become stronger together.
Naruto would probably be really excited. He'd treat Pikachu like a new friend and teammate. He might try to learn all about Pikachu's powers and how it can help in battles. For example, he'd be eager to see Pikachu use Thunderbolt in a fight against an enemy ninja.
Lucario is also a popular choice to be paired with Pikachu in crossovers. Lucario has its own unique abilities related to sensing and combat. When combined with Pikachu's electric attacks, they can form a formidable team. The contrast between Lucario's more serious and stoic nature and Pikachu's cute and energetic personality also adds depth to the story.