A common theme is the power struggle. Castiel is often seen as a more 'pure' angel, while Lucifer is the rebellious one. Their interactions are filled with this underlying battle for dominance or influence. Another theme is redemption. Sometimes Lucifer is portrayed as having a chance at redemption, with Castiel being a key factor in that.
A common theme in such fanfiction is the struggle between Castiel's sense of duty and Lucifer's chaos. Castiel is often seen as a dutiful angel trying to do what's right, while Lucifer represents the breakdown of order. Fanfictions may show Castiel being conflicted when dealing with Lucifer, as he may see some of his own doubts about Heaven's ways reflected in Lucifer's actions.
In some fanfictions, the relationship between Castiel and Lucifer is depicted as a complex rivalry. They both have strong connections to the Winchesters, but for different reasons. Castiel wants to protect them, while Lucifer has his own dark plans. This creates a lot of tension and interesting plotlines where the two angels' paths cross and they engage in battles of wits and power.
One popular 'castiel lucifer fanfic' is 'The Fallen and the Faithful'. It delves into their complex relationship and how they interact in an alternate universe. Another great one could be 'In the Shadows of Heaven', which explores their power dynamics and the moral gray areas between them.
Castiel's relationship with his powers might also change. He may have to limit his use of angelic powers to protect the unborn entity. This can cause internal conflict as he is used to using his powers freely. At the same time, it can also show his growth as a character, as he is willing to sacrifice some of his power for the sake of something new and precious.
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.
In Supernatural fanfiction, Castiel's mind is significant because it's a window into his character development. His mind changes as he forms bonds with Dean and Sam. His thoughts about loyalty, sacrifice, and love are all shaped by his experiences. His mind also holds the key to understanding his unique perspective on the war between angels and demons. For example, he might think about different strategies to end the war that are influenced by his angelic knowledge and new - found human emotions.
Castiel's mind in Supernatural fanfiction is a fascinating topic. His experiences, such as being resurrected multiple times and his interactions with other supernatural beings, shape his mental state. In some fanfictions, his mind is explored through his dreams or hallucinations. These could be manifestations of his subconscious fears and desires. For instance, his fear of losing his friends might appear as a menacing figure in his dreams, representing the threats that constantly surround them in their supernatural adventures.
Perhaps in the fanfiction, Castiel betrays the group because of a misunderstanding. There could be a miscommunication regarding a prophecy or a powerful artifact. He might think that Sam or Dean are going to misuse it and decides to take it for himself to prevent that, but in reality, they had no such intention. This creates a rift between them and is seen as a betrayal.
It shows his vulnerability. Usually, Lucifer is seen as this powerful, menacing figure. But when he cries in fanfiction, it reveals that he has emotions and can be hurt.