There could also be themes of healing. Both characters have had their share of traumas. Lapis was trapped in a mirror and Greg has had his own struggles in life. Fanfiction might explore how they help each other heal and move forward. They could support each other emotionally and in doing so, find new strength within themselves.
You can try searching on fanfiction - specific websites like Archive of Our Own (AO3) or FanFiction.net. Just type in 'lapis lazuli x greg universe fanfiction' in their search bars, and you'll likely find a variety of stories.
One common theme is friendship. Since they are both characters, their relationship as friends is often explored. Another theme could be redemption, perhaps one of them has made a mistake and the other helps them through it.
One common theme is friendship. Since they both have been through a lot, fanfics often explore how they support and understand each other as friends. For example, they might share their past traumas and help each other heal.
A third theme could be the connection between the physical and the spiritual. Lapis lazuli is sometimes seen as a bridge between the two in these light novels. It can represent a way for characters to access a different realm of existence, both in a spiritual and a more tangible sense like a hidden world.
One great 'Steven Universe x Lapis Lazuli' fanfic could be the one where Lapis and Steven go on a journey to discover a new type of gem. It's filled with adventure and character growth. In this fanfic, their relationship deepens as they face challenges together.
One interesting story could be about Lapis Lazuli and Steven going on an adventure together to discover a new gem colony. In this fanfiction, they might face various challenges that test their friendship and understanding of each other.
One great fanfiction could be 'The Bond of Lapis and Peridot'. It explores their relationship in a new adventure on Earth. They face challenges together and their unique personalities play off each other really well in this story.
They're popular because the relationship between Steven and Lapis Lazuli in the show is so complex and full of potential. Fanfic writers can explore different aspects of their friendship or a deeper connection that might not be fully explored in the original series.
Some Steven Universe - dedicated fan forums might have fanfictions as well. Check out places like the Steven Universe Reddit community. Sometimes fans share their own works or recommend good ones there.
One common theme is family. Since they are father and son, a lot of fanfics explore their family bond, how they understand each other, and grow together. For example, stories might show Greg teaching Steven about his human heritage.