Pearl could develop greater courage. In the face of new and unknown situations with the Mystery Girl, she has to be brave. This could transform her from being a bit timid in new social situations to being more confident. For the Mystery Girl, she could develop a sense of loyalty towards Pearl. At first, she might be just a curious figure, but as they go through various events together, she becomes a steadfast friend to Pearl, willing to stand by her side no matter what.
One possible plot could be that Pearl is initially very curious about the Mystery Girl. She might observe her from a distance, trying to figure out her habits and what makes her so mysterious. Then, they could accidentally meet, and at first, Pearl is a bit clumsy in her interaction due to her own insecurities. But as time goes on, they start to bond over shared interests like music or art. The Mystery Girl could introduce Pearl to new aspects of human culture that Pearl has not fully experienced yet.
Perhaps a theme of acceptance. Pearl has her own past and way of dealing with things, and Steven is always so open - hearted. A kiss between them in fanfiction could symbolize Pearl accepting a new side of herself or a new type of relationship. Also, the theme of breaking norms as their relationship in the show is more of a friendship/mentorship, and fanfiction can play with changing that dynamic.
One idea could be that Pearl and Mystery Girl team up to solve a mystery on Earth that involves Gem technology. Maybe they find an ancient Gem artifact that is causing strange phenomena, and they have to figure out how to stop it together.
I haven't read this specific fanfic yet. But generally, in 'Steven Universe' fanfics, Pink Pearl often plays an interesting role. If the 'lemon' in the title refers to a certain kind of fanfic trope, it might involve some more intense or emotional situations. Maybe this fanfic explores the character of Pink Pearl in a new and unique way, perhaps her relationship with other characters in the Steven Universe world.
In a small corner of Beach City, the Mystery Girl set up a little booth selling handmade jewelry. Steven was curious and went to check it out. He saw that the jewelry was made with some unique gemstones that he had never seen before. The Mystery Girl told him that she had collected these stones from all over the world during her travels. As they talked, Steven noticed that she had a small tattoo on her wrist that looked like a gem symbol. He asked her about it, but she just smiled and changed the subject. This made Steven even more determined to uncover the secrets of this fascinating girl.
There might be a fanfiction where Steven and Pearl go on an adventure to a new planet. In this story, they encounter strange new creatures and have to work together to overcome obstacles. It's a great way to explore their characters outside of the main storyline of the show.
One possible theme is growth. Both Peridot and Steven grow throughout the original series, and the fanfic could continue that growth in their relationship. They might learn to understand each other better and become stronger individuals as a result.
One possible plotline could be that Priyanka, being a doctor, has to treat Pearl for some kind of injury. This brings them together and they start to learn about each other's worlds. Another could be that they meet through a mutual acquaintance in a world where the Steven Universe universe and Priyanka's world somehow collide.
A third idea would be to create a story where the Black Pearl has a sentient being inside it. This being could communicate with Steven and the others telepathically. It could be a source of great wisdom or power, but also comes with a dark side that the characters have to deal with. For example, it might try to possess one of the characters in order to achieve its own goals.
One interesting aspect could be the unique character interactions. In many fanfics, new relationships and developments between Steven and Pearl are explored, which might deviate from the original show's plot in creative ways. For example, they could go on adventures that were not part of the canon story.