There could be many interesting plotlines in such a fanfiction. Maybe it could start with a strange accident that leads to Ms Marvel becoming pregnant with Peter Parker's child. For example, some sort of magical or scientific experiment gone wrong. Their relationship would then be tested as they deal with the challenges of an unexpected pregnancy. They would have to face the reactions of their friends and families, like Peter's Aunt May and Ms Marvel's own family. Also, they would need to figure out how to balance their superhero duties with the impending parenthood.
Common themes in 'Captain Marvel pregnant fanfiction' often revolve around her adapting to the new situation. This includes not only physical changes but also emotional ones. There could be themes of her facing new enemies who might target her because of her pregnancy. Additionally, themes related to family, whether it's the father of the child, her own family's reaction, or the idea of creating a new family unit while still being a superhero, are quite prevalent in these types of fan - created stories.
One idea is that Ms Marvel's pregnancy is a result of a time - travel incident. She goes back in time, meets a version of a character she has feelings for, and returns to her own time pregnant. Now she has to deal with the consequences of this unexpected pregnancy, including how it will affect her future as a superhero and the timeline itself.
There might be such fanfiction out there in the vast world of fan - created content, but it's not a common or officially recognized storyline. Fanfiction often explores wild and creative ideas that deviate from the main canon of the characters.
A great 'Marvel pregnant fanfiction' might center around Wanda Maximoff. Maybe she discovers she's pregnant in a world where she's still coming to terms with her powers. The story could explore her fears and hopes for the future of her unborn child, and how her pregnancy affects her relationship with Vision and the other Avengers.
There might be a fanfiction where Ms Marvel's pregnancy is a result of some sort of alien encounter. This could lead to a whole new set of challenges as she has to figure out how to handle her pregnancy in a way that doesn't put the world at risk, all while trying to understand the alien part of it.
I'm sorry, I don't have specific 'Captain Marvel pregnant fanfiction' stories to recommend directly. But you can try looking on fanfiction platforms like Archive of Our Own. There are likely many creative takes on such a concept by various fans, exploring different storylines and character developments within the realm of Captain Marvel being pregnant.
You need to do research on pregnancy in general. Understand the physical and emotional changes. In your fanfiction, you can show how the Marvel character copes with things like morning sickness or mood swings. Also, think about how the other Marvel characters in their world would react. For instance, if it's Thor's wife Sif who is pregnant, how would Thor and the other Asgardians support her? You can create interesting dialogues and scenarios based on this.
One possible storyline could be that they meet during a superhero team - up. As they work together to fight a common enemy, they develop feelings for each other. Eventually, they find out Mrs Marvel is pregnant. This could lead to them having to balance their superhero duties with the impending arrival of their baby. For example, Peter Parker might worry about protecting his family from his enemies while Mrs Marvel could be concerned about how her powers might affect the pregnancy.
In a situation like this, their worlds might collide because of their different support systems. Peter has his friends like Ned and MJ, while Ms Marvel has her own group of friends and family. The pregnancy would mean that these two groups would have to interact. It could lead to some interesting cultural clashes or just general misunderstandings as they all try to figure out how to support the couple. Also, their different powers and how they use them in combat could be affected by the pregnancy. Maybe they would have to develop new strategies together to keep themselves and the baby safe.