Perhaps Ash gets a special ability from a Legendary Pokémon, like the ability to communicate telepathically with all Pokémon. This causes him to be hunted by an organization that wants to use this power for their own gain. With the help of various Legendary Pokémon that he befriends on his journey, Ash has to protect himself and his new power.
One idea could be Ash encountering a Legendary Pokemon that has lost its memory. Ash then tries to help it regain its memories while protecting it from poachers. Another could be a time - travel plot where Ash is sent back in time and has to team up with a Legendary Pokemon to prevent a great disaster from happening in the past that would change the future of the Pokemon world.
One idea could be that Ash discovers a hidden power within himself that allows him to communicate directly with Legendary Pokemon. This power sets him on a journey to understand the secrets of the Legendary Pokemon world. He might start by having an encounter with Mew, who guides him to different places where he can learn more about his new ability.
The unique character development. When a Pok mon is pregnant in a fanfic, it gives an opportunity to explore the Pok mon's personality in a new light. For example, how it copes with the physical and emotional changes. It can also show the relationship between the Pok mon and its trainer in a different way, like increased protectiveness from the trainer.
One plot idea could be that Ash is captured by a new and powerful villain who wants to use his Pokémon knowledge for evil. Another could be that he's captured by a group who mistake him for someone else and he has to prove his identity while trying to escape. Maybe he's captured by an ancient Pokémon that has some sort of grudge against trainers and he has to convince it that not all trainers are bad.
Another interesting plot could be a time - travel story where Ash and Cynthia are sent back in time to the early days of the Pokémon world. They have to adapt to the different rules and ways of training Pokémon back then while also trying to find a way back to their own time.
Another plot could involve a Pokémon contest where May is a contestant and Ash is there to support her. But something goes wrong with the contest rules due to a villain's interference. Ash and May then team up to expose the villain and make sure the contest is fair for all the contestants. It could also be a chance for their relationship to grow deeper as they face challenges together.
Another plot could be set in a world where a strange phenomenon is affecting Pokémon. Ash and Cynthia join forces to investigate. Along the way, they discover a new type of Pokémon evolution that has been hidden for centuries. As they work together, they start to develop a deep friendship that might turn into something more.
A really interesting plot might be that Ash is chosen by an ancient dragon deity to be its champion. As a Dragon Master, he has to go on a quest to collect special dragon orbs scattered across different regions. Each orb gives him new powers or abilities related to dragon Pokémon. Along the journey, he faces challenges from other trainers who also want the orbs for their own purposes.
One plot idea could be that Ash's father was exiled from their town for a crime he didn't commit. The fanfiction could follow his journey to prove his innocence and his attempts to reunite with his family. Along the way, he could encounter unique Pokémon and make new friends who help him in his quest.
Another interesting concept is that Ash is actually a long - lost Jedi in a past life. His connection to Pokémon in his current life is a manifestation of his latent Force abilities. He discovers an ancient lightsaber and starts to remember his Jedi training. His Pokémon friends then become his companions on his journey to restore balance to the Force in both the Star Wars and Pokémon universes.