You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, and you can search specifically for 'Steven x Ruby' fanfiction. There are likely to be many different interpretations and storylines there.
There's a fanfiction where Steven helps Ruby understand human emotions better. In this story, Steven's experiences as a half - human are used to teach Ruby about things like love, friendship, and sacrifice. It shows how their relationship can be a learning experience for both of them.
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.
Some fanfictions might also have themes of redemption or forgiveness. Maybe one of the characters makes a mistake and has to seek forgiveness from the other. This adds an emotional depth to their relationship. Additionally, the theme of unity can be present, where they come together to face a common threat or problem in the steven universe setting.
There are some really cool steven universe ruby lemon fanfictions out there. One that I like is where Ruby and Lemon have an adventure together on a strange planet. They encounter unique creatures and have to work together to overcome challenges. It's a great read if you like seeing their characters in new situations.
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.
A common plotline involves Spinel struggling to fit in on Earth, and Steven being her guide. He shows her the beauty of Earth and its inhabitants. This can lead to a deepening of their relationship as Spinel starts to trust and rely on Steven more. Another plotline could be Spinel having nightmares about her past, and Steven being there to comfort her, which further cements their bond.
The relationship in this fanfiction often explores themes of forgiveness and growth. Steven, with his nature of seeing the good in others, tries to help Spinel move past her pain. Spinel, who has been through so much, slowly starts to open up to Steven. It's a relationship that can be seen as a journey of two broken souls finding comfort in one another.