A common theme is growth. Individually, Kaname and Zero grow as characters. Kaname might become more understanding of the human side, and Zero might become more accepting of the vampire world. And of course, the theme of unity. Their marriage symbolizes the potential unity between vampires and vampire hunters, which could bring peace to their world.
A great fanfiction plot could be that Kaname and Zero get transported to a parallel dimension. In this new world, their usual vampire - hunter roles don't exist. They are just two individuals who meet by chance. As they explore this strange new place together, they start to fall in love.
There's also 'The Married Life of Kaname and Zero'. In this fanfiction, their marriage is shown as a journey of self - discovery for both of them. They learn more about each other's fears and dreams and grow together in their relationship.
In Vampire Knight fanfiction involving Kaname and Zero, there could be various interpretations. One could be a story where their relationship evolves in a world full of vampire politics. They might have to face challenges together against the traditional vampire hierarchy that disapproves of their bond. This could lead to them growing closer and perhaps having a deeper connection that goes beyond the ordinary friendship or rivalry shown in the original series.
I'm not sure specifically about 'Kaname and Zero pregnant fanfiction'. Fanfiction can cover a wide range of themes and scenarios, but it might be a bit of a niche or even an unusual concept. You could try searching on dedicated fanfiction websites like Archive of Our Own or FanFiction.net.
The settings in kaname and zero love fanfiction can also be quite diverse. Some might be set in the same universe as the original story, but with altered events that lead to their love. Others could be completely new and creative settings, like a modern - day AU (alternate universe) where they meet in a completely different context, like at a university or in a workplace. These different settings add more depth and variety to the exploration of their relationship.
In some fanfictions, it might start with a misunderstanding. Zero might think Kaname is behind a series of attacks on the hunters. But as he investigates, he discovers Kaname's innocence. This journey of uncovering the truth brings them closer, and they find themselves falling for each other.
I'm not sure if it's a common type. It depends on the popularity of the original work that Kaname and Zero are from. If the original has a large fan base and a lot of fans are interested in exploring the darker side of the relationship between these two characters, then there might be a fair amount of such fanfiction. But generally, it might not be as common as more positive or mainstream storylines in fanfiction.
Their relationship would become extremely complex. If Zero were pregnant, they would have to rely on each other more. Kaname, who might have been somewhat aloof before, would likely become more protective. Zero, on the other hand, would have to deal with his own feelings of vulnerability and dependence, which could be a big change from his usually tough - guy image.