Redemption and growth are also themes. Maybe Peridot helps Yellow Diamond see a different side of things, leading to her becoming a more empathetic character. Or vice versa, with Yellow Diamond guiding Peridot in some way. It could be about them growing together in an unexpected relationship.
You can try searching on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. There are often specific tags for Steven Universe characters, so you can look for 'Yellow Diamond x Peridot' under the relevant sections.
Their relationship could develop through mutual discovery. For example, Peridot could show Yellow Diamond the unique aspects of Earth that she has come to appreciate. Yellow Diamond, in turn, could share some of her knowledge of the Gem Homeworld with Peridot, creating a bond based on the exchange of ideas.
One common theme is power dynamics. Since Yellow Diamond is a very powerful figure and Peridot is much lower in the hierarchy, their interactions often explore this difference in power. Another theme is redemption. Sometimes, the fanfics will have Yellow Diamond seeking redemption for her past actions, and Peridot plays a role in that process.
I've read a 'peridot x yellow diamond fanfic' where it was set in a post - war scenario. The fanfic delved deep into how they both had to adjust to the new world order. Peridot was trying to find her place among the gems, and Yellow Diamond was dealing with the loss of her authority. Their relationship in this fanfic was a slow - burn type, starting from mutual suspicion to gradually understanding each other. It was really well - written with great character development.
One idea could be a story where Peridot tries to prove her worth to Yellow Diamond in a non - traditional way. Maybe she discovers a new form of energy on Earth that could benefit the Diamond Authority, and she has to convince Yellow Diamond to give her a chance to explore it further.
There's also the 'secret relationship' trope. Considering their status in the Diamond Authority, a relationship between them might have to be kept a secret at first. Fanfictions might explore the challenges and thrills of keeping such a relationship hidden from the other Diamonds and the rest of the Gem society.
You can try searching on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms. Just type in 'Yellow Diamond x Blue Diamond' in the search bar, and it will show you relevant stories.
The world - building aspect. The Gem world they exist in is already so rich. Fanfiction writers can expand on it even more when it comes to Yellow Diamond and Yellow Pearl's relationship. They can create new scenarios, new power struggles, or new forms of loyalty that add depth to the already fascinating world of the Gems.
In some fanfictions, their relationship is shown as a partnership. They each bring different strengths to the table. Yellow Diamond might be more logical and strategic, while Blue Diamond is more in touch with emotions. Writers use this contrast to create interesting dynamics between them, like in the fanfiction 'Diamonds United' where they solve problems together using their respective traits.