It could be about loss and the aftermath. When ash becomes cold, it might symbolize the end of something, like a relationship or a great adventure. So, themes of grief and moving on might be common.
In these fanfictions, a recurring theme is the relationship aspect. If Ash is cold, it can affect his relationships with his Pokémon and his friends. Some stories might focus on how his Pokémon try to warm him up, both literally and figuratively. And his friends might try to break through his cold exterior. There could also be themes related to the challenges he faces because of this 'cold' state, like being underestimated by his opponents in Pokémon battles.
In 'ash becomes red fanfiction', a common theme might also be discovery. Ash could be on a journey to discover the origin or the full extent of his new red state. This could involve him traveling to new places, meeting new characters, and uncovering secrets about himself or the world he lives in. There could also be themes of acceptance, both from himself and from those around him, as he adapts to this new state.
In 'Ash becomes a Lugia' fanfiction, a recurring theme is the clash between Ash's human nature and his new Pokémon form. His human emotions like determination, loyalty, and compassion are still there but are expressed differently as Lugia. Another theme is the exploration of the Pokémon lore. Since Lugia is a very important and mysterious Pokémon, the fanfiction may dig deeper into the myths and legends surrounding it. Additionally, the theme of growth is present. Ash grows not only in terms of power but also in his understanding of the Pokémon universe as he becomes Lugia.
A common theme is the exploration of power. As Ash becomes Mewtwo, he has to deal with a great amount of power that he's not used to. Another theme is identity. He has to figure out who he is now that he's no longer the regular Ash. Also, friendship is often a theme. His friends may have different reactions to his transformation, and he has to navigate those relationships.
A frequent theme in such fanfiction could be adventure. Even as Ashley, the character would still be involved in Pokemon - related adventures. But now, with a different gender, there could be new challenges and opportunities. For example, interactions with other characters, especially of the opposite gender, might change. Also, the theme of self - discovery is quite common. Ashley would need to figure out who she is in this new form and how she fits into the Pokemon world.
One common theme is revenge. After being betrayed, Ash often seeks revenge on those who wronged him, which leads him down the path of evil.
Overcoming challenges is also a major theme. There are always tough opponents and difficult situations in these fics. Ash has to find ways to defeat powerful trainers and deal with various problems that come his way. This shows his perseverance and determination to achieve the champion status.
I'm not sure which specific 'ash becomes cold fanfiction' you're referring to. There are many fanfiction platforms like Archive of Our Own (AO3) and FanFiction.net where you can search for such works using relevant keywords like 'ash becomes cold' in the search bar.
Adventure is also a big theme. Since Ash is known for his adventures, fanfictions often include him and Leaf going on exciting quests together. For example, they might be on a journey to discover a rare Pokémon. This allows for lots of action and exploration in the stories.
One common theme is the struggle between humanity and vampirism. When Ash is involved, it often shows his fight to keep his humanity intact even in the face of vampiric allure.