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.
A theme that often comes up is destiny. Fans like to write about how even as a baby, Eren is already on a path towards his future as a Titan - shifter and a hero. It's about how his early days might be subtly guiding him towards that fate. For example, he might show signs of great strength or determination even as a tiny baby. And also, protection is a theme. His family and those around him are trying to protect him from the harsh reality of the world outside the walls, which is a big part of many baby Eren fanfictions.
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.
One popular type might be those that focus on Levi taking care of Baby Eren in a post - apocalyptic world. For example, stories where Levi has to protect Eren from other threats while also trying to understand his unique powers even at a young age.
The fanfiction might focus on the baby inheriting certain traits from both Levi and Eren. For example, the baby could have Levi's sharp observational skills and Eren's determination. The story could also show how their friends and comrades react to the new addition to their group. Some might be overjoyed, while others might be worried about the implications of having a baby in their dangerous world.
It might develop gradually as Levi helps Eren grow. He would teach Eren things like how to fight, how to be self - sufficient. As Eren learns from Levi, he would start to idolize him. And Levi would see Eren as someone he needs to protect and shape into a good person. Over time, they would become closer, almost like a real father - son duo.
One possible plot could be that Levi takes on the role of a father figure to baby Eren. He might teach Eren about the world they live in, the importance of survival skills, and values like loyalty and courage. For example, Levi could show Eren how to navigate the dangerous terrain outside the walls, all while protecting him from potential threats.