One common theme is family. The appearance of a baby makes Levi and Mikasa form a sort of family unit, and the fanfictions explore how they adapt to this new family dynamic.
The baby could bring them closer. They'd have a new shared responsibility, which would strengthen their bond. They'd be more focused on each other and the family they're creating.
Well, it could start with Mikasa and Eren finding out they're going to have a baby during a time of rebuilding in their world. The story could focus on how they prepare for the baby's arrival. For example, Mikasa knits baby clothes while Eren tries to build a crib. Their friends also get involved, like Armin giving them advice on parenting based on his knowledge. And the baby might grow up with a special connection to the history of the Walls.
One possible plot could be that Eren and Mikasa face many challenges while raising their baby. Maybe they have to deal with threats from outside forces who want to harm their family. They might also struggle with adjusting to their new roles as parents.
Fanfiction.net is also a good place to look. It has a wide range of fanfictions. Just make sure to use the relevant tags like'mikasa', 'levi' and 'baby' to narrow down your search. Sometimes you might need to browse through a few pages to find exactly what you're looking for.
One great mikasa and levi baby fanfiction could be about them adjusting to life as new parents. Maybe they struggle at first with things like sleepless nights but grow closer as they care for their baby.
There could be a fanfiction where Jean and Mikasa's baby has some special abilities. This causes both excitement and worry among them. They have to figure out how to help the baby control these abilities and keep it a secret from those who might want to use the baby for their own purposes.
One popular Levi x Mikasa baby fanfiction might be 'A New Beginning'. In it, they discover a baby and the story unfolds as they take on the role of caregivers. It's really cute as it shows their softer sides.
You should start with creating a setting for your fanfiction. Since they are from a particular world, you can either keep it in that world or create a new one for them. For the story development, think about how the baby changes their relationship. Maybe they become more protective of each other because of the baby. Write in a way that shows the emotions of the characters clearly.