A theme that's quite popular is 'the outsider's perspective'. The OC is usually not part of the hunting world initially, so they provide a fresh view of Sam and his life. Also, 'redemption' can be a theme. Maybe the OC has a troubled past, and Sam helps them find a new path, or vice versa.
There's also the theme of 'shared destiny'. In many fanfictions, it seems like Sam and the OC are fated to meet and be together. Their paths cross in unexpected ways, and they end up having a big impact on each other's lives. For example, they might be the key to solving a major mystery that neither could solve alone.
One common theme is 'forbidden love'. Since Sam has his hunter duties, a relationship with an OC can be seen as something that goes against the rules of his world. Another theme is 'finding strength in each other'. The OC often brings out a different side of Sam, and they help each other grow and face challenges.
Well, healing is a big theme. The age - regression can be a way for Sam to heal from past traumas in many fanfictions. Also, relationship building. The OC and Sam form a special bond during this time. For example, in some stories, the OC helps Sam learn things anew, like how to trust again or how to have fun without the weight of his usual responsibilities. This creates a deep connection between them that forms the core of the story.
Well, family is a huge theme. It's not just about Sam and Dean, but also their extended family and how that impacts their lives. Sacrifice is also common. They are always willing to put themselves in harm's way for each other or for the greater good. And then there's the theme of the unknown. Fanfiction often takes them into uncharted territories in the supernatural world, exploring things that the show might not have covered yet.
One common theme is the balance between family life and hunting. Sam has to figure out how to be a good husband while still going out and fighting the supernatural. Another theme is the impact on his relationships, like with Dean. His marriage can cause some tension or growth in their brotherly bond. Also, the idea of starting a new life with someone is often explored, like building a home and having a normal life despite his hunting past.
One popular theme could be the relationship between Sam and the OC (original character). It might explore how the OC becomes part of Sam's world, perhaps in a hunting adventure. Another theme could be family - how the OC fits into the Winchester family dynamic. And sometimes, there are themes of self - discovery for the OC with Sam as a guiding figure.
The theme of redemption is also present. The OC may have made mistakes in their past, and through their adventures with the Winchesters, they seek to redeem themselves. This could be related to accidentally causing harm in the supernatural world or having a dark past that they are trying to overcome.
A theme of self - discovery is also common. Bella has her journey of self - discovery in the Twilight series, and Sam has his in Supernatural. In fanfiction, their paths of self - discovery might intersect, and they could learn from each other. For instance, Sam could teach Bella more about the wider supernatural world, and Bella could show Sam how to be more in touch with his emotions like she is with hers in her own story.
A sense of duty is present as well. Dean feels it's his duty to keep Sam safe. So when Sam is hurt, it's like he's failed in his mission. This leads to self - reflection in Dean and often a new determination to keep Sam out of harm's way in the future.
The theme of family legacy is quite prevalent. Since they come from a family of hunters, many fanfictions explore how this family history affects their actions and decisions. Also, the theme of growing up in a tough environment is common. They face a lot of hardships at a young age, and fanfictions often depict how they cope with it and become stronger.
Since I don't actively engage with this type of fanfiction, I can't say for sure. But generally in fanfiction, themes might include the intense emotional connection between the characters, perhaps with a romantic or sexual undertone.
One common theme is the exploration of their deep emotional bond in a romantic context. Since they already have a strong brotherly bond in the original show, fanfictions often build on that to create a more intimate, romantic relationship.