Love is a very common theme. Their relationship is often explored in-depth, from the early days of their meeting to their deep, abiding love as Garnet. Another theme is loyalty. They are always there for each other, and this loyalty is highlighted in many fanfictions. For example, in stories where they face challenges together, their loyalty to each other never wavers.
One popular Ruby x Sapphire fanfiction is 'A Tale of Two Gems'. It beautifully explores their relationship with lots of sweet and tender moments. Another great one could be 'Ruby and Sapphire: Bonded Hearts' which delves deeper into how they support each other in different situations. And there's also 'The Ruby - Sapphire Union' that shows their journey together in a really creative way.
In the context of the show, since Sapphire is in a relationship with Ruby, if we consider the concept of a 'father' in a non - traditional sense, Ruby could be seen as the co - parent. Gems don't reproduce in the same way as humans, but their relationship could be the equivalent of a parental unit in this fanfiction.
In a 'Steven Universe Sapphire Pregnant' fanfiction, perhaps the pregnancy is unexpected. Sapphire could start having premonitions about the future of their unborn child. The story might focus on how the other characters in the show react to the news. Some might be overjoyed, like Pearl who loves new life among the Gems, while others could be more cautious, thinking about the potential dangers in their world.
The unique relationships. Ruby and Sapphire's love for each other and their new role as parents to Baby Steven create a lot of interesting story possibilities. Their different personalities also add depth. Ruby is more fiery and impulsive while Sapphire is calm and collected, and seeing how they interact with Baby Steven, who has his own charm, is fascinating.
The relationship can be developed through shared adventures. For example, they could go on a quest to find a rare gemstone that has special significance for all of them. During this journey, they would have to rely on each other's strengths, which would deepen their bond.
To develop their relationship, you could explore their past. Maybe there were times when they first fused into Garnet and had doubts about each other. By delving into these memories and how they overcame them, it can strengthen their relationship in the fanfic. Also, having them face new challenges together, like dealing with a new type of gem enemy, and seeing how they support each other through it.
One plot idea could be that Sapphire and Ruby are having a disagreement about how to best protect Steven. Sapphire, with her future vision, sees a potential threat approaching in a very different way than Ruby does. This leads to some tension between them as they try to figure out the best course of action for Steven's safety.
You can try fanfiction websites like Archive of Our Own (AO3). There are a lot of talented writers who create stories about Ruby, Sapphire and Baby Steven. Just use the search function on the site and type in relevant keywords, and you'll be presented with a variety of fanfictions to choose from.
In the fanfiction, Ruby and Sapphire could be having trouble adjusting to life in a new town. Steven, who has experience with change, could introduce them to new friends and show them all the fun things about the place. Meanwhile, they could teach Steven more about their unique Gem culture, like how they fuse and their special powers. This would create a story full of cultural exchange and friendship building.