One common theme is probably adventure. Ben is known for his adventures in the original series, and in fanfiction with the Null Fairy, they might go on new quests together. Another theme could be friendship or partnership. How Ben and the Null Fairy work together, support each other, and grow their relationship is often explored.
Since I'm not familiar with a lot of 'null fairy fanfiction', it's hard to say for sure. But in general fairy - related fanfiction often has themes like magic, otherworldly powers, and a connection to nature. So perhaps in 'null fairy fanfiction' there could be some sort of unique take on these, or it might involve a 'null' concept which could mean a lack of something normal for fairies, like a lack of wings or a lack of magic in a particular context.
I'm not sure of specific 'Ben 10 Null Fairy' fanfiction titles off the top of my head. But if you join some Ben 10 fan communities on social media platforms like Reddit or Facebook groups dedicated to Ben 10, you can ask the members there. They are usually very passionate and would be able to point you to some great fanfictions about the Null Fairy. They might even share their own works if they have written any related to it.
A common theme is adventure. Since the original show is about Ben having adventures with his alien forms, fanfictions often continue this trend with Gwen also being involved in exciting escapades.
I don't recommend delving into the themes of lemon fanfiction. But for regular Ben and Gwen - related fanfiction, themes can be things like loyalty. They are always there for each other during their battles against aliens. Another theme could be their evolving relationship as they get older and face more complex situations in the series. Also, their individual character development, like Ben becoming more responsible and Gwen getting stronger with her powers, are often explored.
One common theme is growth. Both Ben and Gwen grow as individuals and in their relationship. Another theme is friendship, as their bond is often a central part of the stories. Adventure is also a big theme, since they are from the Ben 10 universe and usually go on exciting adventures together.
Common themes in Ben and Gwen romance fanfiction include the idea of secret love. They might keep their feelings hidden from the rest of the family or friends. Also, the theme of self - discovery is present. As they explore their romantic feelings for each other, they also learn more about themselves. And sometimes, there's a theme of sacrifice, where they are willing to give up something for the sake of their relationship.
One common theme is empowerment. Since it's about a female taking on the role of Ben 10, it often shows how she can be just as strong, if not stronger, than the male counterpart. Another theme is friendship. She usually has to rely on her friends to help her in her adventures.
I'm not entirely sure about the common themes in 'Ben 10 lemon fanfiction' as I haven't studied it deeply. But it might include things like character relationships, new adventures for Ben and his aliens, and maybe some alternate universes.
One common theme is love. Since Ben and Mal are often seen as a couple, many fanfictions explore their romantic relationship. Another theme is adventure. They go on different quests or face challenges together. For example, in some fanfictions, they might have to save Auradon from a new threat. And a third common theme is self - discovery. They learn more about themselves through their interactions with each other.
Friendship is a very common theme. Many fanfictions explore how Ben and Evie support each other through different situations, like in school or during royal events. Another theme is personal growth. For example, Evie might grow in her confidence in her fashion design skills while Ben could grow in his leadership abilities with Evie's help.