Another theme could be humor. The idea of Danny, a male character, crossdressing can lead to some really funny situations in the fanfic. For instance, how his friends react or the misunderstandings that might occur. Also, it could be used as a way to subvert gender norms within the context of the Danny Phantom universe. Maybe he uses it as a disguise to outwit his enemies.
Love against all odds is a big theme too. Since it's a gay relationship in the context of Danny Phantom, there are usually obstacles like the expectations of the town or the fear of being ostracized. And also, the theme of friendship - how his friends react to his new relationship can be a major part of the story. Sometimes they are supportive, other times they need time to adjust.
I'm not sure of specific crossdressing Danny Phantom fanfics off the top of my head. But you can try searching on fanfic platforms like Archive of Our Own. There might be some interesting ones there.
Another theme is friendship and loyalty. The relationship between the reader and Danny is usually based on these qualities. They support each other through tough times, like when Danny is facing a really tough ghost or when the reader is having problems in their normal life. In some fanfics, this friendship can even develop into a romantic relationship over time.
Another theme is power struggle. Danny has his own set of powers, but when interacting with other ghosts, there can be a battle for dominance or control. This adds a lot of action and drama to the fanfics.
Friendship is a very common theme. These fanfics often explore the deep bond between Danny and Tucker, how they support each other through thick and thin. For example, in many stories, Tucker uses his tech knowledge to help Danny in his battles against ghosts.
One common theme is redemption. Since Desiree is often a villain in the original show, many fanfics explore her path to redemption, with Danny playing a crucial role in it.
One common theme is friendship development. Since they have different personalities in the original work, fanfics often explore how they can become friends. Another theme could be rivalry turned partnership, where they start off as rivals but end up working together.
One common theme is power adaptation. Danny has to adapt his ghost powers to the rules and challenges of the My Hero Academia world. Another is identity, as he has to balance his two identities - his human self and his ghost self - in a new and different hero -centric environment.
There are several common themes in 'danny phantom x pariah dark fanfic'. Firstly, the struggle for control. Pariah Dark's immense power makes him a threat to Danny's world, and Danny has to find a way to either stop him or control his actions. Secondly, the exploration of the supernatural world. Both characters are deeply rooted in the supernatural, and fanfics often expand on the rules and mysteries of that world. Thirdly, the idea of heroism and sacrifice. Danny may have to make sacrifices to protect his world from Pariah Dark, and these fanfics can really dig deep into what it means to be a hero in such a dangerous situation.
One common theme is the power struggle. Ember has her own set of powers and often tries to overpower Danny, either for her own gain or just for the fun of it. So there's a constant back - and - forth in terms of who's in control.