One common theme is resilience. Dean has to be strong and keep fighting even though he's blind. Another theme is the importance of his relationships, like with Sam and Castiel. They support him through his difficulties.
The theme of hope is quite common. Despite his blindness, there's always a sense of hope that he'll be able to overcome the challenges. Then there's the theme of sacrifice. Dean may have to sacrifice certain things in order to keep fighting the supernatural while being blind. And the exploration of his vulnerability is also a theme. It shows a different side of Dean that we don't often see in the original series, which makes these fanfictions really interesting.
Overcoming challenges is also a big theme. Being blind in a world full of dangerous supernatural entities means facing many difficulties. So, the fanfiction usually shows how the character rises above these obstacles, which can be very inspiring.
Another theme is loyalty. Benny is often depicted as being extremely loyal to Dean, and Dean in turn has to grapple with his loyalty to Benny in the face of other hunters' suspicions. There are many stories where this loyalty is tested.
One common theme is the idea of partnership. Since Bella and Dean come from different backgrounds, their partnership in facing supernatural threats is often explored. Another theme is self - discovery. Bella might learn more about herself as she gets involved in the dangerous world that Dean is used to.
One common theme is Dean's loyalty. Fanfictions often highlight his unwavering loyalty to his family, especially Sam. For example, in many stories, he'll go to great lengths to protect Sam from any danger.
One common theme is mentorship. Dean often takes on the role of teaching Jack about the world, hunting, and how to control his powers.
Redemption is also a big theme. Many fanfictions focus on Dean trying to break free from his demon self and find a way back to being good. It could involve him facing his past actions as a demon and making amends. Another theme is the relationships he has. His bond with Sam might be strained or strengthened in different ways. And of course, there are often romantic themes as well, whether it's a relationship with a female character from the show or an original character. The idea of Dean being a demon also often leads to power - related themes, like how he uses or abuses his newfound demonic powers.
A lot of these fanfictions explore Dean's relationships while he's sick. His bond with Castiel could be deepened as Cas tries to heal him using his angelic powers. Or his relationship with his father might be revisited, thinking about how his dad would have reacted. It adds emotional depth to the story.
Another theme could be the danger and mystery that often surrounds the supernatural elements in the show, but now in the context of Dean's pregnancy. For example, there could be a plot where the cause of the mpreg is some sort of dark magic or a new, unknown entity, and Dean and the gang have to figure out how to deal with it while also ensuring the safety of the unborn child. This adds an extra layer of drama and adventure to the story.
The theme of identity is also important. Dean is constantly struggling with his identity as a hunter, a brother, and a son. Anna, on the other hand, may be dealing with her identity as an angel who has fallen or is on the verge of falling. In fanfiction, their relationship can help them both come to terms with who they are. For instance, through their interactions, Dean might learn to accept the parts of himself he's been denying, and Anna might find a new purpose in her existence that is more in line with her true self.
A lot of fanfictions focus on Dean's romantic relationships. This could be with characters from the show like Castiel, exploring the complex and often debated relationship between them. Or it could be with original characters created by the fanfiction writers. These romantic themes often add an extra layer of drama and emotion to the stories. Also, themes of sacrifice and heroism are quite common as Dean is often portrayed as a heroic figure in the Supernatural universe.