Well, one aspect could be the unique relationship between Peridot and Steven in the fanfic. Peridot is such an interesting character with her growth and development throughout the series, and when paired with Steven, there can be many new storylines. Maybe it focuses on their friendship deepening into something more, or perhaps it's about them going on adventures together that are different from the main plot of the show.
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.
I'm not entirely sure which specific 'Steven Universe Lapis x Steven Lemon Fanfic' you are referring to. There could be many interpretations and themes within such a fan - created story. It might explore the relationship between Lapis and Steven in a unique way, perhaps with elements of friendship, adventure, or even some emotional growth for the characters.
The fanfiction 'The Crystal Gems and Spinel' also features a great relationship between Steven and Spinel. In this one, they work together with the Crystal Gems to protect the Earth from a new threat, and their friendship blossoms during the process.
A really interesting plot twist in these fanfics can be when Spinel gets corrupted again, but this time Steven has to find a completely different way to heal her. It challenges his usual methods and tests their relationship. Another plot twist could be that Spinel starts to have dreams or visions about Steven's future, and she has to decide whether to tell him or keep it a secret. This can lead to a lot of internal conflict for Spinel and also affect her relationship with Steven in unexpected ways.
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 popular 'Steven Universe Connie x Steven fanfic' is 'Together Forever'. It beautifully captures their relationship's growth. It shows how they support each other through different challenges on Earth and in space adventures. The characterizations are really on point, staying true to the original series.
Adventure is also a common theme. They go on different quests or face various threats together. This could be something like exploring an ancient gem ruin on Earth or fighting off a new enemy. The theme of acceptance is important too. Accepting each other's flaws and differences. Amethyst accepting Steven's sometimes naive view of the world, and Steven accepting Amethyst's wilder side.
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.