Another theme could be the struggle against the supernatural world. The reader - character might be thrust into the world of vampires and have to deal with the rules, dangers, and secrets that come with it, all while maintaining their relationship with Edward. It adds an element of drama and conflict to the story.
Love and passion are also very common. Given that it's a 'lemon' (which often implies a more sexual or romantic - intense nature), the fanfictions usually delve deep into the emotional and physical connection between the two characters. This can include things like longing, desire, and the challenges of being in a relationship with someone so different.
One common theme is forbidden love. Since Edward is a vampire and the OC is an original character, their relationship often faces obstacles just like in the original Twilight. Their different natures make their love seem impossible at times.
Another option could be to look for dedicated Twilight fanfiction communities or forums. Sometimes, fans share their own works or recommend good 'edward cullen x reader' fanfictions there. However, not all of them may be of high quality, so you need to do some screening.
One common theme is the forbidden love aspect. Since Carlisle is a vampire and there are many differences between him and a human reader, it often creates a sense of forbidden attraction. Another theme is the idea of salvation. The reader might be in a bad place in life and Carlisle becomes a sort of savior figure.
One common theme is the exploration of an unconventional relationship. Since it's a male OC with Edward Cullen, it goes against the typical heterosexual relationships in the original Twilight. Another theme is self - discovery. The male OC often discovers new aspects of himself while being involved with Edward.
One common theme is the clash of two different worlds. Edward comes from the Twilight world which is centered around vampires and werewolves, while Harry is from the wizarding world. Fanfictions often explore how these two very distinct settings and cultures interact.
One great 'Edward Cullen x Reader Fanfiction' is 'A New Beginning'. It shows the reader character moving to Forks and having an unexpected encounter with Edward. Another is 'Love in the Shadows' which delves deep into the relationship between the two, exploring how they deal with the challenges of Edward's vampire nature. And 'Unforeseen Bond' is also popular as it focuses on the emotional connection that develops between them.
One common theme is rivalry turned friendship. Given their initial animosity in the Twilight series, many fanfictions explore how they might overcome their differences and become friends or even more. Another theme is the protection of Bella. They both care about her deeply in the original story, and in fanfictions, this can lead to situations where they have to work together for her sake.
One common theme is the clash of different cultures. Harry Potter comes from a world of magic with wizards, spells, and Hogwarts, while Edward Cullen is from the world of vampires in Twilight. The fanfictions often explore how these two very different cultures interact.
In 'Edward Cullen x fem Harry Potter fanfiction', a common theme is the adaptation of the characters to a new environment. For example, if Edward were to enter the world of Hogwarts, how would he adapt? And vice versa for the fem Harry Potter in the Twilight world. Another theme is the discovery of new abilities or a combination of abilities. Maybe the fem Harry Potter could learn something from Edward's vampiric abilities and incorporate it into her magic. And the theme of loyalty is also there. How loyal would they be to their own original worlds and friends while developing a relationship with each other?
One common theme is the exploration of Edward's supernatural abilities in relation to the reader. For example, how he uses his powers to protect the reader from other supernatural threats.