Love and attraction can sometimes be a theme as well, though not always in a romantic way. It could be more about admiration and respect for each other's skills as pokemon trainers. For example, the female character might admire Ash's determination, and Ash might be impressed by her unique training methods.
One common theme is the change in relationships. For example, her relationships with male characters like Brock and Gary might be different. There could be more of a romantic undertone in some cases. Another theme is the different approach to Pokemon training. A female Ash might be more nurturing or have a different battle style.
One common theme is friendship. Ash forms strong friendships with female characters and their pokemon. For example, his bond with Serena's Fennekin as it evolves. Another theme is adventure. They go on various adventures exploring new areas and facing tough opponents.
One common theme is Ash's growth. Writers like to show how he matures from a novice trainer to a more experienced and wiser one. Another theme is friendship. His relationships with his Pokemon and human friends are often explored, like how they support each other in tough times.
The discovery of new Pokemon species is also a common theme. Writers like to create new and unique Pokemon for Ash to encounter. This adds an element of surprise and adventure to the fanfiction, as Ash has to figure out how to interact with and potentially catch these new Pokemon.
One common theme is adventure. Ash and the Pokemon mothers often go on adventures together. Another is relationship building, exploring how Ash interacts with all the different Pokemon mothers in this harem - like setting.
Protection is also a big theme. Often, Ash has to protect the female legendary Pokemon from villains who want to capture or harm it. This shows Ash's heroic side and also the vulnerability of the legendary Pokemon. In some stories, the female legendary Pokemon also protects Ash in return, highlighting the mutual care between them.
A common theme is friendship. The female Charizard forms deep friendships with other Pokémon in Ash's team. Another theme is growth, as she evolves not just in strength but also in character throughout the story.
Since I don't encourage or promote such fanfictions that might be inappropriate, I can't accurately state the common themes. However, in general Pokemon fanfictions, common themes include friendship, growth, and the pursuit of Pokemon championships.
One common theme is friendship. Since Ash is at the center, his relationships with the pokemon mothers in the harem often involve elements of friendship that develop into something more. Another theme could be adventure. Ash's journey in the pokemon world is filled with adventures, and this is often incorporated into these fanfictions as well.
One common theme is family. Since Delia is Ash's mother, the fanfiction often emphasizes the family bond between them. Another theme could be growth. Ash grows as a Pokemon trainer, and Delia might grow in her understanding of Ash's world.