A common theme is the exploration of new powers. Since Ash becomes a Lucario, the fanfics often focus on him learning to use abilities like Aura Sphere or Extreme Speed. Another theme is identity. Ash has to come to terms with being a different Pokemon and how that changes his relationship with his friends and his role in the Pokemon world.
Well, one theme is the adaptation to a new body. In these fanfics, Ash as a Lucario has to get used to a different physical form, different senses. For example, he might be more attuned to Aura now. Also, friendship is a big theme. His friends' reactions to his transformation can range from shock to acceptance, and how they support him through this change is often explored in these stories.
There's a fanfic series that I heard about where Ash turns into a Lucario gradually. It starts with some strange symptoms and then he fully transforms. This fanfic is unique because it focuses on Ash's internal struggle with his new form. He has to learn to control his new Lucario abilities while still being himself, and it also shows how his friends react to his change in a very realistic way.
Well, in 'ash and fem lucario' fanfiction, there's often the theme of protection. Ash may feel the need to protect Fem Lucario, and in turn, Fem Lucario might protect Ash from harm. This could be especially prominent in dangerous situations like facing off against a villainous team. Additionally, the theme of acceptance is common. Ash accepts Fem Lucario for who she is, with all her strengths and weaknesses, and Fem Lucario does the same for Ash. This acceptance forms the basis of their relationship and drives the story forward in many cases.
Friendship is a very common theme. Since they are like brothers, their strong bond and loyalty to each other is often explored. Another theme is growth. They grow as individuals while also strengthening their relationship as they face different challenges.
Some 'female Lucario' fanfics focus on her role in a team. Whether it's a team of Pokémon or a combined team of Pokémon and humans, her skills and how she contributes to the group's success can be a central theme. There are also fanfics that deal with the mystery and lore surrounding Lucario in general, and how the female Lucario fits into that.
One common theme is adventure. They might go on a journey together through the Pokémon world, facing various challenges. Another is friendship evolving into something more. The bond between Ash and the female Lucario grows deeper over time.
In 'ash turns into a gardevoir fanfic', the theme of identity crisis is quite common. Ash has been a human trainer for so long, and suddenly becoming a Gardevoir shakes his sense of self. He may question who he is now and where he belongs. Additionally, the theme of transformation itself is explored, not just the physical change but also the mental and emotional shifts that come with it. For instance, how does his perception of the Pokemon world change? Does he view his own Pokemon differently now? These are all aspects that are often delved into in such fanfics.
A theme that often comes up is the reaction of others. His friends, like Pikachu and Misty, might be shocked or scared at first when they see Ash as Mewtwo. Also, there's the theme of adaptation. Ash has to adapt to his new form, which may be very different physically and mentally from his original self. For example, he might have to get used to Mewtwo's telepathic abilities and the way he moves.
A common theme is the exploration of the Pokémon world from a different perspective. As an Eevee, Ash sees things in a new light. He experiences the Pokémon world on a more intimate level, like understanding the language of Pokémon better. There's also the theme of adaptation. He has to quickly adapt to his new physical form, which includes learning to move, run, and use his new Eevee - specific abilities.
Well, in these fanfictions, a frequent theme is identity. Ash has to grapple with his new identity as Arceus. He's no longer just a regular Pokémon trainer. Also, the theme of sacrifice is common. There's usually something that led to his transformation, which might have involved sacrificing something he held dear. Additionally, many of these fanfictions touch on the theme of change. His transformation into Arceus brings about changes in his relationships with his Pokémon friends and other trainers in the world.
Another theme is friendship evolving into love. A lot of these fanfics start with Ash and Aria being friends or acquaintances and then their relationship deepens over time. For example, they might help each other out in tough situations, which leads to stronger feelings. It's a really sweet and common trope in these fanfics.