One common theme could be identity. Since there's a 'double' aspect, it might explore how characters deal with having two different identities or versions of themselves. Another could be duality, like good vs. evil if the double represents two opposing moral stances.
Love and relationships are common themes. Just like in the original Twilight, the fanfictions often explore the complex love between different characters. For example, how they overcome obstacles in their relationships.
One common theme is identity. Since it's about double life, characters (either trainers or pokemon) often struggle with who they really are. Another theme is secrecy. There's always something hidden about their second life. For example, a pokemon might be a powerful guardian in its other life but just a normal pokemon in the eyes of its trainer.
Love is a very common theme, just like in the original 'Twilight' series. But in fanfiction, it might be explored in different ways, such as forbidden love between characters other than Bella and Edward. Another common theme is the exploration of powers. Since the vampires and werewolves in 'Twilight' have unique abilities, fanfictions may expand on how these powers interact or develop further.
One common theme could be friendship. Since they are characters, their relationship might be explored in terms of how they become friends or support each other.
Another theme might be about relationships. These stories can show how the two sexes communicate, love, and sometimes conflict with each other in various settings, such as in a romantic relationship or in a work - related context. For example, in a story, a male and a female colleague may have different approaches to a project due to their different genders, and through their cooperation, they learn from each other and grow both personally and professionally.
One common theme is loyalty. Since the characters are double agents, they constantly struggle with where their true loyalties lie, whether it's to the good side like the Order of the Phoenix or the dark side like the Death Eaters. Another theme is secrecy. They have to keep their double identity a secret which adds a lot of tension to the story.
One common theme could be friendship. They might explore how Kevin and Double D's relationship evolves from just acquaintances to really good friends. Another theme could be adventure, where they go on some exciting journey together.
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One common theme is secrecy. Characters in these novels often go to great lengths to hide their other lives. For example, in 'Dr. Jekyll and Mr. Hyde', Dr. Jekyll has to keep the existence of Mr. Hyde a secret from everyone around him.