One possibility could be that in this fanfiction, Ash discovers the Spearow in a unique situation. Maybe it was injured and Ash helped it, leading to a strong bond. The Spearow could then have unique abilities that help Ash in his Pokemon journey, like being able to fly faster than other flying - type Pokemon in his team.
The plot could involve Ash finding the Spearow when it's lost. Ash takes it under his wing and starts training it. The Spearow might be stubborn at first, but as Ash shows patience, it begins to listen. Together, they enter battles and the Spearow surprises everyone with its unique battle style.
Another cool new partner for Ash in fanfiction could be Riolu. Riolu is strong and has the ability to sense auras. It could learn a lot from Ash and Pikachu and grow into a powerful Lucario. This would give Ash a Pokémon with great combat skills and a unique ability that could help in battles and in understanding other Pokémon's emotions.
One storyline could be about Ash finding a lost and injured Pokémon as his new partner. For example, if his new partner is a Togepi. He could nurse it back to health and in the process, form a strong bond. As Togepi grows, it could learn new moves and help Ash in gym battles, especially against fairy - type opponents.
Ash would be terrified. He is facing a group of Spearow without his most reliable Pokémon by his side. He would also feel disappointed in Pikachu. After all the adventures they've had together, he never expected Pikachu to leave him in such a dangerous situation. He might start to doubt their friendship and partnership.
Begin with Ash's character. Consider his growth and development throughout the Pokemon series. You could write about a time when Ash has to face his biggest fears in a new Pokemon world. It could be a world where the rules of Pokemon battles are different, forcing him to adapt in new ways.
A great Ash new Pokemon fanfiction often has a unique plot. For example, Ash could be transported to a parallel Pokemon universe where he has to learn new battle strategies. Good character development is also key. Show how Ash changes and grows in response to new challenges.
Some fanfictions might show Ash becoming a sort of honorary Pokemon Ranger. He would then have to balance his duties as a Trainer and as a Ranger. This could create internal conflict for him as he tries to decide which role is more important at different times. His friends from the Pokemon journey, like Brock and Misty, could also be involved, adding more layers to the story.
Well, Ash is no stranger to adapting to new situations. In these fanfictions, he first tries to understand the basic principles of how Beyblade and Pokemon can work together. He might study the different types of Beyblade parts and how they can interact with the abilities of his Pokemon. He also asks for advice from other more experienced trainers. Once he has a basic understanding, he starts training his Pokemon to work in harmony with the Beyblade elements. He practices new battle strategies that incorporate both Pokemon moves and Beyblade spins. He also has to learn how to handle the new equipment, like how to launch a Beyblade in a way that complements his Pokemon's attacks. In addition, he builds relationships with his Pokemon in a new way, as they now have to cooperate in a different kind of battle environment.
There could be a new rival for Ash. This rival might have a very different approach to Pokemon training, like focusing more on the beauty and grace of Pokemon rather than just battle strength.