Another plot could be that the reader has a special power that attracts Spinel's attention. They end up on an adventure together to figure out the origin of this power. Along the way, they face various challenges and in the process, their relationship deepens as they rely on each other for support.
Maybe the reader is a human who can somehow communicate with gems. Spinel, feeling lonely after her past experiences, meets the reader. They start to bond over sharing their feelings and fears, like Spinel opening up about her abandonment issues and the reader sharing their insecurities about fitting in.
One idea could be that the reader is a new gem on Earth and Spinel is initially suspicious but then they become friends through exploring human culture together. For example, they could go to a carnival and Spinel discovers the joy of cotton candy.
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.
There could be a fanfiction where Spinel teams up with Steven to explore different dimensions. They encounter strange new gems and have to use their combined powers to overcome challenges. This would show their growth and the development of their friendship. Spinel's unique abilities would add an exciting dynamic to their adventures.
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.
To write a believable relationship, show the development gradually. Start with Spinel's initial reaction to the reader, which could be curiosity or wariness. Then, have them interact in small ways, like sharing a simple conversation or a small task. For instance, if they are working together to fix something in Little Homeworld.
Fanfics that deal with Spinel's redemption arc are also very popular. After all the pain she has been through, seeing her slowly heal and find a place in the world of Steven Universe is heartwarming. Some writers create scenarios where Spinel helps other characters who are also dealing with their own traumas, which adds an extra layer of depth to 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.
Perhaps Steven finds himself in a situation where he has to protect a number of characters, and in the process, they all fall for him. Like he could be on a mission to save some of the corrupted Gems, and as he heals them, they see his pure intentions and are drawn to him. This could lead to a harem where they all vie for his attention in different ways, some being more shy and others more bold in their affections.
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.
One popular theme is redemption. Spinel has a troubled past, and many fanfictions focus on her journey towards redemption with Steven's help. For example, stories where Spinel tries to make up for her past actions.
One idea could be that the OC is a new gem who arrives on Earth and Lapis is initially suspicious but gradually warms up to them as they show their kind nature. For example, the OC might help Lapis with her water powers, like finding new ways to control and shape water in a more creative way.