One key element is the relationship dynamic. Dean is often portrayed as the protector of baby Castiel. For example, in many stories, Dean will go to great lengths to keep Castiel safe from harm.
Another element is the setting. Often, they are on the move, just like in the show. The 'Baby' (the car) is a central part of the setting. It serves as a safe haven for them and also a place where many of their interactions and character - developing moments happen. The stories might take them to different spooky or strange locations, which adds to the overall atmosphere of the fanfiction.
The exploration of Castiel's new form is also important. His 'baby' form brings a sense of innocence and vulnerability. Writers often use this to show his growth and development as he experiences things in this new state, like learning about human things through Dean's guidance.
There's also 'Dean, Castiel and Baby: A New Bond'. This fanfiction focuses on how Castiel, in his new 'baby' form, starts to understand human emotions better through his interactions with Dean. It has a unique take on their relationship and is quite engaging.
Castiel first wakes Dean gently from the nightmare. Then he sits with Dean and tells him stories about the great heroes in Heaven. He tells Dean that he is also a hero, and that no nightmare can ever truly harm him because Castiel will always be there to protect him. He strokes Dean's hair softly as he talks, which calms Dean down.
The relationship between Dean and Castiel is of course central. Their dynamic, whether it's a budding romance or a deep friendship, is explored against the backdrop of the shooting star motif. Writers use the idea of a shooting star to add a touch of magic and mystery to their interactions.
In dean - castiel relationship in such fanfiction, there's often a deep emotional connection. They might show a side of extreme vulnerability towards each other. Their relationship can be intense, with a lot of passion and a sense of 'destined to be together' kind of feeling.
Sam would probably be very protective. He has always been there for Dean, and now with a new addition to the family in the form of a baby, he would see it as his responsibility to keep the baby safe. He might also be a bit of a mentor, teaching the baby about the world of hunting and how to handle different supernatural creatures.
It could be about Castiel taking on a fatherly role for Dean. Maybe in the story, Dean has nightmares often, and Castiel is there to comfort him like a daddy would. For example, Castiel could use his angelic powers to soothe Dean's troubled mind during those nightmare - filled nights.
The theme of family or a found family could be prominent. Despite not being related by blood, Castiel acting as a daddy to Dean creates a family - like bond. Also, the theme of healing is possible. If the nightmares are a result of emotional wounds, then the story could be about how Dean heals with Castiel's help.
The baby could have the power of teleportation. Since both Dean and Castiel are involved in a world full of supernatural elements, teleportation would be a useful power. It could help the baby escape dangerous situations or quickly reach its parents when they are in trouble.
One common theme is friendship. Their bond, whether it's a platonic friendship or something more, is often explored. Writers like to show how they support each other through tough times.
A good Castiel and Dean fanfiction often has strong character portrayals. Since fans are already familiar with these characters, it's important that they are written true to their personalities. For example, Dean's tough - guy exterior with a soft heart, and Castiel's somewhat naive yet powerful nature.