Steven is an obvious choice. Their relationship has so much potential for growth and exploration in fanfiction. Steven's kindness and ability to forgive can really help Spinel on her journey of self - discovery.
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.
A Steven x Spinel lemon fanfiction is likely to be a work that explores a romantic or perhaps more intense relationship between Steven and Spinel in a rather spicy or detailed way. However, such fanfictions often deviate from the original canon of the story. They can be interesting in terms of exploring different character dynamics and emotions that might not be shown in the official series. But they also might not be to everyone's taste as they can sometimes push the boundaries of what is considered appropriate in the context of the original work.
In some fanfictions, Spinel might become more confident. After leaving her past behind, she could start to believe in herself more and not let others' opinions bring her down as easily.
Love and acceptance is another common theme. The fanfictions may show how Steven accepts Spinel for who she is, flaws and all, and how Spinel learns to love and be loved in return. This can be in a platonic or a more romantic sense, depending on the story.
One great Spinel x Steven Universe fanfiction is 'A New Bond'. It beautifully explores the relationship between Spinel and Steven as they navigate their complex feelings. The story has really well - written dialogues that bring out the unique personalities of both characters.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including Steven Universe. Just use the search bar and type in 'Spinel x Steven' to find relevant stories.