Well, a common theme is the exploration of the unexpected. Pregnancy is not something you'd typically associate with Peter Parker, so these fanfictions often look at how he copes with this sudden and strange situation. Also, themes of sacrifice might come up. He may have to sacrifice some of his superhero activities or personal time to deal with the pregnancy. And of course, there's the theme of growth, both as a person and as a hero, as he faces this new challenge.
One common theme could be the challenges of a relationship between two characters from different universes. With Rogue's power - absorbing ability and Peter Parker's spider - like powers, there could be issues related to how they interact physically. Another theme might be the reactions of their respective friends and allies to the pregnancy.
One common theme is the clash of their different backgrounds. Peter is young and relatively new to the superhero world, while Black Widow has a lot of past experiences. Another theme could be how they handle the responsibilities of a new life coming.
Another theme is the struggle between normal life and superhero life. Peter has to deal with school, homework, and teenage problems while also being Spider - Man. Fanfictions often show how he manages to juggle these two very different aspects of his existence.
One common theme is his relationship with other characters in the Spider - Man universe, like his interactions with Tony Stark or Ned Leeds while being in a 'bottom' role. It often explores the more vulnerable and emotional side of Peter.
One common theme is self - discovery. As Peter is a transgirl, she has to figure out who she really is and come to terms with her identity. Another theme is acceptance, both self - acceptance and acceptance from others like her friends and family. There's also the theme of balancing her new identity with her superhero life. How can she be Spider - Man while also being true to herself as a transgirl? And often, there's a theme of facing discrimination or misunderstanding in society due to her being transgender and a superhero at the same time.
Another theme is the use of Peter's scientific knowledge. Since he's a genius, in these fanfictions, he often uses his knowledge to innovate in his business as a CEO and also to create new gadgets for his superhero activities. For example, he might develop new web - shooter designs in his company's lab.
One common theme is identity crisis. Peter has to deal with being both Peter Parker and Spider - Man, and dissociation often makes this divide even more pronounced. Another theme is isolation. As he dissociates, he may feel more alone in his struggles.
One common theme is the discovery of powers. As a child, Peter is just starting to figure out what he can do, and this journey of discovery is often explored. Another theme is friendship. How his relationships with his peers, like Ned in later years, might have started when he was a child.
Love is a very common theme. Since they are a couple, fanfictions often explore the depth of their love for each other. Another common theme is the struggle between Peter's life as Spider - Man and his relationship with MJ. It shows how MJ deals with Peter's double life.
One common theme could be self - acceptance. Peter dealing with his new body type and learning to love himself despite the changes. Another might be how his relationships, like with his friends or MJ, are affected.