It's not appropriate at all. Pokemon has a positive and clean image, and creating such erotic content related to its characters, like gym leaders, would be disrespectful to the brand and its fans. It also violates the moral and ethical standards expected in the fan community.
Obviously Ash is one of the most popular characters. And then there are the gym leaders like Brock, Misty (who also has gym - related aspects in some versions), and other gym leaders from different regions.
One idea could be that Ash uses his unique battle style which he has developed over his journey to create a really challenging gym. He might include Pokémon from all the regions he has visited in his gym battles, making it a diverse and exciting experience for trainers. For example, he could have Pikachu lead the charge as always, but also include some of his less common Pokémon like Heracross or Gliscor.
Well, it could be about Lanora challenging Ash to a gym battle. And during the battle, they start to respect each other's skills. Maybe Lanora realizes Ash's determination and they become friends.
The main characters are Lanora and Ash. Lanora, as a gym leader, has her own set of Pokémon and rules in the gym. Ash, on the other hand, is on his journey to become a Pokémon master. In this fanfiction, their paths cross and they interact, which forms the core of the story.
Well, in some ash gym leader fanfiction, there could be a story where Ash has to overcome personal challenges while facing a gym leader. Maybe he's feeling unconfident, but through his Pokémon's loyalty and his own determination, he manages to pull through. The gym leader might also have their own backstory that ties into the battle, making it more than just a fight for a badge.
One popular pairing is Ash x Misty. Misty is a Gym Leader and she has a long - standing relationship with Ash in the Pokémon series, so it's often explored in fanfiction.
His understanding of Pokémon could deepen further. Since he now has to design challenges for trainers, he would study Pokémon types and abilities more intensively. He might discover new strategies and combinations that he hadn't thought of during his regular journey. This could also make him more respected in the Pokémon community as a knowledgeable gym leader.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions on various topics, including Ash x Gym Leader ones. Just use the search function and type in relevant keywords.
" Wilderness Challenge " was a novel about urban life, written by a local warrior. The story told the story of Chen Xu, as the world's most awesome wilderness streamer, surviving and livestreaming in various wilderness areas. This book was completed and had 1046 chapters. It was a VIP work signed by Qidian Chinese Network and could be read and purchased for free. In the novel, Chen Xu live-streamed in different scenarios, from Mount Everest to the Beirut Triangle, from the Desert of Death to the Swallow Cave, showing the beauty and danger of the wilderness. The novel has been completed. There are a total of 1014 chapters and can be read on the Creation Chinese Network.