Well, in many Cas and Dean first kiss fanfictions, it often occurs in a moment of high emotion. Maybe after they've just saved each other from a dangerous situation. The writers usually build up a lot of tension between them first. For example, there might be lingering looks and unspoken feelings for a long time before that first kiss. It's a way to explore their relationship deeper than what's shown in the original series.
A lot of Cas and Dean first kiss fanfictions also set the scene in a more private and intimate setting. It might be in the bunker where they live, late at night when they are the only two there. The kiss is described as gentle at first, as if they are both a bit hesitant, but then it deepens as they realize how much they've been longing for this moment.
I really like 'The Kiss in the Rain'. It's a bit of a classic in the dean and cas fanfiction world. The rain - soaked setting for their kiss adds a lot of drama and emotion. The story around it also does a good job of showing how their relationship has evolved over time.
One common theme is the struggle with their identities. Both Dean and Cas have complex identities and in many fanfictions, their kiss is a moment of acceptance of themselves and each other. For example, Cas coming to terms with his feelings as an angel while having human - like emotions for Dean.
One common theme is the revelation of hidden feelings. For a long time, they may have been suppressing their emotions for each other, and the first kiss is like the breaking of a dam. Another theme is the acceptance of a new aspect of their relationship. It's not just about being friends or hunting partners anymore. And finally, there's often a sense of new beginnings, as if this kiss opens up a whole new world of possibilities for their relationship.
One popular trope is the 'hurt/comfort' scenario. For example, Dean gets injured on a hunt, and Cas takes care of him, which leads to a tender moment and a kiss. It plays on the emotional bond between them and the protectiveness they feel for each other.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a vast collection of Supernatural fanfictions, and you're likely to find many stories about Cas and Dean with their romantic moments. Just use the search function and type in relevant keywords.
The idea of 'forbidden love' is also common. Maybe because of their different natures (Dean being a hunter and Cas being an angel), or because of some external forces like the rules of their respective groups. This adds an extra layer of drama to the story. And of course, there's the theme of pure, unadulterated love where the kiss is just a beautiful expression of their deep feelings for each other.
One great fanfiction is 'AUs and What-Ifs'. It explores different alternate universes for Cas and Dean. It's really interesting as it shows their relationship in various scenarios that the show didn't touch on. Another one is 'The Road Less Traveled' which delves deep into their emotional bond and how they face challenges together outside of the main plot of the series.
One popular theme is the friendship - to - more relationship. Fans often explore how their deep bond could develop into something romantic. Another theme is their battles together against the supernatural. Writers love to describe their teamwork and how they rely on each other in dangerous situations.
The character development is often a great feature. Writers can really explore Dean and Cas in ways that the original show might not have had time for. They can dig deep into their personalities and how they interact with each other on a more intimate level.
Another theme is sacrifice. Given the nature of the Supernatural world, they often put themselves in harm's way for each other. Fanfictions play on this selfless aspect of their relationship. For example, Cas might sacrifice his grace to save Dean, or Dean might risk his life to rescue Cas. It shows the depth of their bond.