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.
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 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.
One common theme is friendship. Their bond is often explored, like how they support each other through tough times. Another is adventure. They are often put in exciting situations where they have to use their wits and skills.
Love and its complexity is a very common theme. Their relationship can be romantic, platonic or a complex mix of both. Also, the struggle between the light and dark side of the Force within them and how they influence each other's choices is frequently explored. In many fanfictions, they are both trying to find a balance between their different natures. For example, in some stories, Rey helps Ben resist the dark side, while Ben helps Rey understand the darker aspects of the Force without being consumed by it. And of course, the theme of destiny and how their fates are intertwined is also quite popular.
One common theme is power combination. Since Naruto has his own chakra - based powers and then getting the Omnitrix, how he combines these two power sources. Another theme could be identity. Naruto has to deal with being a ninja and also having the ability to transform into an alien, which might make him question who he really is.
One common theme is redemption. Ben's journey towards redemption is often explored in relation to Rey. Another theme is the power of love, how their connection might change the course of the galaxy.