A common theme is redemption. Shadow often has a past he wants to atone for, and Silver can play a part in that journey. For example, in some fanfics, Silver helps Shadow see the good in himself again.
One common theme is friendship. Despite their differences, Sonic, Shadow, and Silver often come together in these fanfictions to face a common enemy or achieve a common goal. Another theme is the exploration of their individual powers and how they can complement each other.
Some fanfictions might explore a more emotional side of their relationship. Maybe Silver is having trouble controlling his powers and Shadow, who has his own inner demons, helps him. They could have heart - to - heart conversations about their pasts, their loneliness, and how they can move forward. This kind of story can really dig deep into their characters and show a different aspect of their relationship.
Another theme could be adventure - based. Given that they are from the Sonic universe which is full of action and adventure, the fanfiction might incorporate their relationship while they are on a quest or facing a common enemy. They might start off as reluctant allies and gradually develop deeper feelings for each other during the course of the adventure.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, and you can easily search for Shadow x Silver fanfiction using the search bar.
One great story could be 'The Mysterious Bond' where Shadow and Silver form an unexpected alliance in a world filled with chaos and they discover a magical lemon tree that has special powers. It's a really interesting take on their relationship.
Well, 'Silver's Shadow' is also a popular one. It focuses on how Silver's powers interact with Shadow's more brooding nature. It's full of action scenes where they team up against common enemies and their relationship develops throughout the story.
Well, there's a fanfiction called 'Sonic, Shadow and Silver: United'. In this one, they form an unexpected alliance. It shows Sonic's speed, Shadow's power, and Silver's psychic abilities working together in really interesting ways. There are also some great character development moments for all three of them.
Another reason is the creativity of the plots. Since it's fan - made, there are no real boundaries. A story could combine elements from different Sonic games or even introduce entirely new concepts. For example, a fanfic could have Shadow and Silver discover a new form of Chaos energy that changes the power balance in their world.