One idea could be Ash discovers a rare fire - type Pokémon that has powers beyond normal. He has to train it while facing challenges from Team Rocket who also want the Pokémon. Another plot could be Ash enters a fire - type Pokémon tournament and has to use his mastery of fire - types to defeat tough opponents.
A really exciting plot could be that Ash is somehow transported to a parallel universe where the rules of fire - type Pokémon are different. He has to quickly adapt and learn these new rules in order to survive and find his way back home. He might meet alternate versions of his friends and enemies there. Along the way, he uses his existing skills with fire - type Pokémon but also discovers new abilities that he can bring back to his own world.
Well, perhaps Ash travels to a region where there are ancient fire - type Pokémon that have been long forgotten. He stumbles upon their hidden lair and tries to form a bond with them. This could lead to him having to protect these Pokémon from poachers who want to sell them on the black market. Also, a plot could involve Ash having to help a young trainer with a fire - type Pokémon that has some behavioral issues. He uses his experience and knowledge of fire - types to solve the problem.
One idea could be that Ash discovers a hidden power within himself that allows him to communicate telepathically with dragons. This new ability helps him in battles and also in understanding the dragons' needs better.
Ash can be developed by showing his growth in understanding different fire - type Pokémon's unique needs. For example, learning how to train a Charmander that is more stubborn than others. This shows his patience and adaptability as a trainer.
One idea could be Percy discovers a new power related to fire that was dormant within him. Maybe it was a gift from an ancient and forgotten god. He then has to learn to control it without the help of his usual mentors like Chiron.
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.
In Si as Ash Pokemon fanfiction, a prevalent plot is Si being a rival to Ash at first but then becoming his closest ally. They could compete in Pokemon battles and then team up against a greater threat, like an evil organization trying to capture all the rare Pokemon. There might also be a plot where Si discovers a hidden power within Ash that even Ash himself doesn't know about, and they work together to harness that power for the good of the Pokemon world.
Maybe Bayleef gets separated from Ash during a storm. It then has to find its way back to him through a dangerous area filled with traps set by Team Rocket. Along the way, Bayleef makes new friends who help it on its journey back to Ash.
One idea could be focusing on how Ash's friends react to the news. They might be shocked at first but then rally around to support her. Another could be Ash dealing with the physical and emotional changes during pregnancy while still trying to pursue her goals.
A more heart - warming plot could be Riolu being initially afraid of its own strength and Ash helping it to gain confidence. Maybe Riolu accidentally causes some damage and is scared of using its power again. Ash then trains with it in a special way to show Riolu that its strength can be used for good. This could involve some cute and touching moments between the two as they build a stronger bond.
Well, perhaps in the 'ash in a dress fanfiction', Ash is forced to wear a dress as a punishment by a mischievous Pokemon. This leads to him having to learn new ways of moving and interacting while in the dress. He could also end up starting a new trend among the Pokemon, where they all want to wear dresses like him for fun.
Some plot ideas might include Ash and Hoopa teaming up to rescue a group of Pokémon that have been captured by an evil organization. Hoopa could use its portals to get into the enemy's lair. Another plot could be that Hoopa gets sick, and Ash has to find a way to heal it. He travels far and wide, meeting different Pokémon and people who might have the cure. And there could be a story where Hoopa reveals a hidden world to Ash, a world full of ancient Pokémon and secrets. Ash then has to explore this world with Hoopa and make sure these secrets don't fall into the wrong hands.